Don't know about airwire, but I have, still running every ops session, the first r/c battery Bachmann Shay.
I started saving certain bits that are removed inside the tender several years ago, think I have 50 of them now, so in the last several years I've done 50, most all with sound.
One issue is flicker.
Not a problem on older units, but on new ones, Bachmann in their infinite wisdom placed the flicker driver (and smoke unit voltage regulator) on the HUGE pre-Ames Super Socket in the tender, and it has to go.
If you use Sierra, you can drive the flicker from that, or buy a Miniatronix driver or some other brand.
The wires from the third truck to the second are......well.....puny.
First one done, by a local, turned on the power and smoke.
Logical spot for batteries is in third truck.
Throttle and sound in second (fuel bunker) truck area.
Same board in fuel bunker as on later 2-truck Shay, goes in the junk box.
I have much better plugs and super-flex wire, the male part is the same pin spacing as the JST plug they used, and will solder right in.
Like with all recent units, seems to take a bit of extra work, but works fine when done.
I use incandescent bulbs, 4 or 4.5AH NiMH batteries, Sierra and a 6-amp throttle, since I know from experience a 3-truck Shay on a grade, with a load, can draw more than 4 amps.
Remember to tie down the wires in the fuel bunker as delineated in the review in GR if running track power.
I have converted-with Airwire- a good number of the 3 truck shays and many many dozens of the two truck units with either Airwire or RCS hardware. The three truck unit is a fine loco, and is a perfect candidate for electronics, sound, battery pack -everything- on board. There are some issues with the wire harness that require upgrading, but the loco is certainly one of the smoothest runners when done. Plenty of space for all that is needed with exceptional run times .