It's been some time but I finally completed my testing of the PC/PCI or otherwise called SB-Link header on the P5A. I'm glad to report that it works (tested on a YMF724).
- There is no need to play with interrupt settings in your BIOS. This pertains to SETUPDS 3.16 - it doesn't care which interrupt your card is actually on. You can be running in ACPI with all devices on IRQ11, it works just fine (and many boards of that era did offer an ACPI BIOS later on, as did the P5A). Don't make any IRQ reservations for "legacy" devices or anything special like that. The only thing you need to be sure to do is select an IRQ other than the one your card is actually reports being on in your startup screen when you configure SETUPDS.
- INTA# mode doesn't make use of the SB-Link header. If you have it working in this mode, you are not using serialized IRQ. To be clear: If you're getting a 'cannot detect' message in SETUPDS, one of several things could be causing it. Your cable could be plugged in wrong, or what is less probable, perhaps your SB-Link header isn't actually functional.
- I don't know what the "ISA" setting is in SETUPDS. I could not get it to work on a BX board (though I did not try it on the P5A), and I'm not sure if it makes use of serialized IRQ (i.e. the SB-Link connector) either. Documentation is sparse, but perhaps someone here could elaborate on it.
All this said -- my testing was limited to the SETUPDS utility. I didn't test any games or anything like that, so I'm not aware of any quirks with SB-Link and the Aladdin V chipset. SETUPDS 3.16 supports this chipset without any modification. My testing was confirmed by running SETUPDS with the cable both inserted and removed. When removed, I received a 'cannot detect' when trying to use S-IRQ mode (though INTA# did work without the cable). When it was inserted, it allowed selection of S-IRQ and the sound demos played fine.