I was wondering the same thing, if the secondary IDE port was a possibility. Actually I think it is possible without disabling audio, at least on IO's with the Yamaha audio chip. From what I remember, the Yamaha chip is on the ISA bus and the built-in AC97 is not used.
From page 18 of the 686A datasheet:
"System Address Bus. SA[19-16] are connected to ISA bus SA[19-16] directly. SA[19-17] are also connected to LA[19-17] of the ISA bus. If the audio interface is disabled (SPKR pin strapped low), SA[15-0] are connected directly to ISA address bus pins SA[15-0] (the audio interface pins are used for the IDE secondary data bus). If the audio interface is enabled (SPKR pin strapped high), SA[15-0] are multiplexed with the IDE Secondary Data Bus. In this case, SA[15-0] may be connected to both SDD[15-0] and ISA bus SA[15-0]."
And from page 19, description of SPKR:
"Speaker Drive. Output of internal timer/counter 2. Also functions as a strap input sampled at reset to determine the function of the Audio / Game interface pins: 0=Disable Audio / Game interface (pins used for IDE Secondary Data Bus SDD[15-0]; ISA SA[15-0] pins used for ISA bus only), 1=Enable Audio / Game interface (pins used for Audio/Game functions; SDD[15-0] multiplexed with ISA SA[15-0] with SOE# / MASTER# as 245 OE# / DIR control.)."
I'm no EE, but it looks like your choices are IDE Secondary muxed with ISA bus OR Audio-Game muxed with ISA bus.