Regarding  "Can you use both approach and Nav buttons at the same time?"  I
have an article here from "The Stec Pilot" which is published by Stec.  The
particular issue I have is September 1996.  In this issue a Scott Howard
wrote an article that said with Systems 40s,50s and 55s you can use both
functions to give much better GPS tracking.  On the system 60s (I have a
60-2) there is a wiring modification that you can make so that when you are
in Nav mode and your tracking GPS the autopilot automatically goes into the
high gain mode as if its in the approach mode.  When you switch to VOR the
autopilot goes back to the low gain mode unless you are in the approach mode.
 The implication in the article in the article is that you can't use both
buttons at the same time on the 60 series of autopilots.

Tom Byrnes Lancair IV 99.999% with 4% to go