I haven’t done a GTX to Allstar as a permanent thing though a few years back I did experiment with it. Audio and PTT aside (those are easy) COS is the problem. You can program a pin to switch when a valid COS/PL come in, but I could not get it to reset. So…I looked at the speaker lines. When a valid signal comes in the Audio chip turns on. And there is DC on the speaker lines which is why you cant have a grounded speaker. But what I used was a resistor isolated input to the URI for COS. I may have made is a voltage divider, don’t remember.
FWIW, re the other note about RX bandwidth, the reason I was playing with it was to see if a GTX could be used as a repeater receiver. Well with the normal preselector no way, but I dropped in a pair of Toyo filters for the right range. That did work but had to fiddle with the VCO
Hope this helps
GeorgeC W2DB 2360, 28599