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- the PT3 Turbo Sound Player (6 channels) is a translation/conversion from the Z80 code from Sergei Bulba. 
The CPU time is huge during decoding. so do not expect to use it concretely for a fullscreen demo!

- the ROUT (OUT routine) function used in US3T is a special version using 4 AY! So requires 2 Mockingboard.
It is a routine trying to respect at best the right / left split of the channels of a PT3.
Because of the wiring of the Mockingboard (compared to the Spectrum world), with an Apple II + Mockingboard, it is impossible to respect the ABC split (concretely channel A on the left, B on the middle and C on the right). The three channels of the first AY are all wired to left. And the second AY is wired to right.
So using 2 AY (= one Mockingboard), we can manage to simulate the correct stereo:
- channel A => channel 1 * first AY            / nothing on channel 1 * second AY
- channel B => channel 2 * first AY            / channel 2 * second AY
- channel C => nothing on channel 3 * first AY / channel 3 * second AY
This is the method used in MAD EFFECT #2...

Here, with a PT3 with 6 channels, so we have to use 4 AY to get the same result, using the same trick!

- in the source code (PTS.a), there is a second ROUT routine (commented) requiring only 1 Mockingboard. 
Obviously the split of the channels will not be optimal!

- The sync part of the code to display mixed MODES (3 different modes here) uses a new technique with several interrupts.
Obviously, each tick of a PT3 player does not have a constant CPU use, hence the use of tricks to keep the synchronization on each display frame!
Again AIPC is struggling but a special version could be build for this emulator (see source code)

- I do not mention the other emulators because to my knowledge, on PC, only APPLEWIN and AIPC support 50Hz mode. 
And this release requires a 50Hz machine...

- The PT3 version is not a conversion from the XM original file but a total rewrite of the song for the AY.