I've just installed my Audiophile2496 to my new Athlon system. (Athlon XP2000+, Abit NF7 mobo, 512RAM, WinXP)
works like a charm. I don't even have to tweak anything.
BTW, I don't think M-audio says anything about not supporting Athlon. They just have some statements about AMD and VIA configuration issues. To be safe, just don't get a VIA mobo.
Intel, or AMD/Via Chipset all the way. I am using a 66 with an nForce (A7N8X-Deluxe), and had to give up on using SATA drives with the system. The Sil Controller does not mate well with the Delta at all, due to bad PCI bus implementation in the nForce system. Nothing has managed to fix it except for buying two new IDE hard drives and run a separate install on them only for recording, with the SATA array invisible.
So if you ever plan to move to Sata drives, go with Intel, or if you want the knockout punch of price performance of AMD, get the Via KT880 chipset boards, which perform just as well as the nForce and have native SATA southbridges.