OK I see some things..
Right off the bat, you should clock the AY-3-8910 off of M2 (aka "phi 2") on the NES. Do not use an external oscillator.
I drew up a circuit that "should" work with the AY-3-8910. There's no reason it won't work (crosses fingers). It uses two chips, a 74139 dual 2 to 4 line decoder, and 7402 quad NOR gate. It should work fine. You cannot read from the AY-3-891x chip but this is fine- you'd get a bus conflict if you tried with the ROM anyways.
http://tripoint.org/kevtris/mappers/inc ... ksound.jpg
Stuff marked "NES" connects to the NES cart. The setup is pretty simple- the 74139 decodes WRITES to C000-FFFF using the first half of the chip, then the second half decodes C000-DFFF and E000-FFFF sections.
The NOR gates then converts the enables into a form the AY-3-891x likes. And that's about it.
The 1uF cap and diode form a power-on reset circuit (the capacitor value might have to be lowered... say 0.1 uf or even 0.01uf depending on how fast the game decides to write to the chip after powerup. 1uF is safe in any event, tho you may have to hit reset once or twice on your NES.
If all goes well, you need to connect the following to the NES cart board:
D0-D7, R/W, M2, /CE (for PRG ROM), A13, A14, 5 volts, and ground.
If anyone else makes one of these, I suggest using an AY-3-8912 if you have it, simply because it's 28 pins instead of 40. Most of the pins aren't used since they are two 8 bit I/O ports.
audio resistors.... I am not sure what values to use. The original poster used what looks like 1K? resistors between all the audio outputs, and then a 3K resistor to 5V. For an audio coupling cap, .1 uf to 10uF is fine.