I'm pretty sure the GPS is just a standard GPS receiver that sends the data to the VX-8. You could probably use any GPS if you can make an interface cable for it. You'd have to figure out the pinouts on the mic plug to do it.
The APRS functionality on the radio is pretty much full functionality. You can see other stations, as well as their location, speed, text, symbol, everything. You can also send and receive text messages, receive messages from a particular message group, etc. Send me an APRS message if you want.
I'll take some pics tonight of the APRS screens and post them so people can see what it looks like.
A guy at work bought some sort of module that plugs into his HT. I can't find exactly what he has, but it is relatively small with a blue plastic case.
It's probably the TinyTrak:
Byonics - TinyTrak4 GPS Position Encoder
The thing about having the GPS for this radio that makes it valuable is that it totally automates the APRS functionality. What I mean by that is with the GPS attached, the radio will automatically take your position, speed, etc. and use that for the beacon information. Then you can tell it to auto-beacon every xx seconds or minutes. Without the GPS, you have to punch in all the information yourself every time and beacon manually. The GPS is a little pricey but it's worth it for the convenience, if you really intend to use APRS.
Aside from APRS, is there any real reason to even consider the Kenwood? At this point, the only real thing that interests me in the Kenwood is the expanded receiver. But I'm starting to think, why bother?
Well, if you want full 5 watts on 220mhz. The kenwood hears a little better on 220, also. IMO, the VX-8 is a better radio, though. If we forget about the GPS/APRS stuff and just focus on the radio functions, the Yaeusu beats it, IMO. People have told me that the TX audio sounds better. The radio is
A LOT tougher and it's waterproof. It's relatively easy to program. It's triple receiver is amazing (two ham VFO's + broadcast, all at the same time!). It comes pre-programmed with "special" memory banks for VHF Marine, SWL, and WX. The way that it allows you to have different settings for each VFO is really nice.
I liked the Kenwood for as long as I had it, but after I had this new Yaesu for a while, I was hooked. I already sold the THF-6a.