Hello Jim,
The three-band MTR I believe is unfortunately not PSK-able. I think only the two-bander is. I sold mine to Ray.. You might be able to find a used one on Ebay, but they do not come up very often, since so few were made. You might want to ask Steve Weber about it to make sure though. There is also the AT_Sprint Yahoo group.
I never made a contact on PSK with the MTR, but tried only once.. Not sure if Ray ever tried it.. It did send and receive though, I just didn't try much.
If you want to do PSK31, you might want to look for a Small Wonder Labs PSK20 or Warbler transceiver; also discontinued, but they show up sometimes. I got the last one, and it works really well, but no CW.
Maybe your solution is to sell your wife on Morse code as something fun to do.. You could also get a K42 CW Keyboard/Reader Kit:
http://k1el.tripod.com/K42_C.html and use it with the regular MTR. The advantage in this case is that the other side doesn't need a PSK-able rig. That would also allow you to talk to your wife using a CW rig while she uses the K42 with another one.
Good luck,
Gil.