Getting the highest level of performance out of your MXT requires the best accessories. As the MXT has been on the market for almost 5 years, there are a lot of good coils, headphones and other equipment on the being produced that can really improve your detector's ability to find the treasure you are seeking.  Again, I have no affiliation with any of these makers, these are just my opinions about the products below.

3) Kelleyco

2) Jimmy Sierra Coils:

12 Round Concentric Hotshot - Similar to the standard, open center coil that comes with the MXT, but larger. I have not used one, bu I would expect that it might have problems with ground noise and overload on high mineral soils, and as these are common in my area, I was not interested in this coil.

25 Round Concentric Magnum Force - Similar to the standard open center coil that comes with the MXT, but much, much larger! It's the "Big Daddy" of the deep searching loops. This gigantic loop was designed for use by Cache and Relic Hunters working in low mineral soils. The 25" Magnum Force loop sacrifices small target sensitivity for increased depth, and is best suited for finding targets of coffee can size or larger (definitely not a nugget hunting coil!). However, on large targets in low mineral soil it will achieve depths up to 3 to 5 feet depending on the size of the target. This loop is a favorite among Relic Hunters. Accurate discrimination is also lost and the 25" loop should only be used in the "all metal" mode following the instructions enclosed with it. Because of its size it is also heavier than other coils, so for ease of operation, an  Arm Support System is included with purchase of the 25" loop.

5 inch EXcelerator - Like White's small round coil, this coil is good for ghost towns, trashy areas with low to moderate soil mineralization. It is good for areas needing tight separation of junk from good targets. Good for small targets like earrings. Also like whites, the Kellyco EXcelerator coils are Waterproof, and submersible for shallow water hunting.

8 inch EXcelerator - This is similar in size the stock coil, being a general purpose coil.  Best for use detecting deep targets in areas with low to moderate soil mineralization and little trash or junk. It takes some time with your detector to get the hang of fast pinpointing with this coil. Like the standard coil, this would be a poor choice for most nugget shooting applications because it is very sensitive to hotrocks and mineralization. Like the coils by Whites, the Kellyco EXcelerator coils are Waterproof, and submersible for shallow water hunting.

12.5" EXcelerator Searchcoil -  One of the first "Increased Size" search coils, and while I have not had experience with this coil, I would expect using the 12.5" to generally result in adding about 25% increased depth versus a standard factory search coil under most low mineral situations. It would also be expected to be a bit less sensitive to smaller objects.  The Kellyco12.5, 14 and 18" coils are all a round, open loop design.

14" EXcelerator Searchcoil - Reports from detector owners who have tested and used these coils have shown outstanding results in the large number of coins, rings, jewelry and relics recovered in areas that were heavily worked over by many different detectors. Not only have they seen increased sensitivity on smaller, deeper items but the coil goes substantially deeper to find coins, rings and other treasures. The 14" is going much deeper than standard coils. Some actual field test results show double the depth compared to other comparable coils. The EXcelerator performs better!! The Kellyco 12.5, 14 and 18" coils are all a round, open loop design.

18" EXcelerator Searchcoil - This large 18" EXcelerator Search coil is the largest of the series, and would be expected to be more sensitive to mineralization, less sensitive to small objects but provide increased depth of detection and ground coverage. In high mineral soils it would be necessary to turn down the gain significantly to stabilize the response (thereby losing some of the increased depth).  The Kellyco 12.5, 14 and 18" coils are all a round, open loop design.

Part II: Pinpointers for the MXT:

I've never been a real big fan of pinpoiters. Some people like them - I really don't see much need for them. With good training and experience, you should be able to center the coil on the target and pinpoint it accurately. Pinpointers for the MXT come in two types, the separate unit kind which is good for any metal detector, and the attachable small probe type, as made by Sun Ray. The standard separate unit type is often not very sensitive, and are easily lost. I find they slow me down in target recovery more than speed me up.

Sun Ray Invader DX-1 Target Probe: The DX-1 Target Probe is made to satisfy the pinpointing and retrieval needs of DFX/MXT users.  It  will accurately pinpoint on coin size targets up to 2"+ deep depending on detector used, settings, ground and moisture conditions. It consists of a light weight, waterproof/submersible 9" X 1" diameter probe which mounts on top of upper shaft. DX-1 probe and cable weigh approx. 6 oz. DX-1 switch box, connectors,  cable and two probe clips, etc. weigh approx. 5 oz. - approx. 11 oz total. While the probes are waterproof, the switch box is only water resistant and must not be submersed (it uses the same kind of electrical connectors as White's). The probe incorporates all of the same functions as the stock coil including accurate visual and audible target ID along with identical pinpoint functions. It attaches to the detector shaft and a toggle switch shuts off coil as it turns probe on and vise versa. Coil and probe are never on at the same time. There are no external buzzers, vibrators or lights are needed as all target responses are heard clearly through your detector headphones. No extra batteries are required , as the probe utilizes the detectors power source. 

Part III: Headphones for the MXT

Nearly all users will want to use some sort of headphone with their MXT. There are many reasons for this. One is that you will be far better able to hear how a target sounds through headphones, which after practice, makes a big difference in detecting marginal targets. Also, most better headphones have a volume control. There is no direct volume control adjustment on the MXT. Finally, the beeps, chirps and other noises made by the MXT can be annoying to others when working in public areas like parks. So while headphones can be rather hot in warm weather, they are pretty much a necessity in my opinion.

The headphones that come with the MXT are good basic units and are reasonably functional. It is not absolutely necessary to get other headphones but there are better ones on the market and it may be worthwhile to get a pair.