cometguy --
I think CBAILEY makes a very good point...if your soil is AT ALL mineralized (which most are -- except for "young" soils such as are found in "farmland" areas such as parts of the midwest, and places like Florida), then the FBS units are close to unbeatable in terms of ID on deeper coins. It has to do with the multi-frequencies...a single-frequency VLF machine CAN compete, ID-wise, with the FBS units in VERY GOOD/MILD soil -- and can absolutely surpass them in terms of depth. BUT -- if you want to ID coins to maximum depth, the FBS units cannot be beat in my experience, in anything but the most mild of soils. I have never tried an X-Terra, so can't say for sure, but I have tested MANY VLF units, and NONE of the ones I've tested surpass FBS in that ONE aspect -- accurate ID with depth.
Having said that, if you really, really don't like the multi tones, and don't think you can ever get used to them, then a switch is certainly worth considering. I will say this, though...the "language" of the Explorers takes awhile to learn, but for most users, the multi-tones eventually turn out to be an ASSET, not a liability. But everyone is different, and if you really don't see yourself "growing into" the multi tones, they it is definitely something to think about.
I will say one more thing...which you may not know but may help you out. That is, you CAN reduce the number of tones on your Explorer; that's what variability does (in theory, anyway...I haven't personally tried it). Variability set to maximum (10) gives you the maximum number of tones which get assigned to different ID numbers. If you lower that, you are lowering the number of tones that you are allowing the machine to utilize -- i.e. lumping more ID numbers into a tone. The lower the variability, the larger the range of ID values you are shoving into a lesser number of tones. If you set variability to "1," (the minimum) I'm pretty sure that you have now set your machine to use a single tone for ALL ID values (not POSITIVE, though, as I haven't tried it; I always have run my variability at "max," but I think what I am telling you is accurate). Likewise I am pretty sure that choosing a variability number just above the minimum of 1 -- say, 2, or 3, would result in just a few tones used by the machine for the entire range of ID values. You might find that a variability of, say, 3, will give you, essentially, a "four-tone" machine...
Hope this helps...
Steve