Aubrey Hodges, the soundtrack composer for Doom 64, also made the soundtrack for Quake and Quake 2 on the N64 as well. Can these be downloaded somewhere and used with Darkplaces (Quake) and KMQuake 2?

Both soundtracks are available on Aubrey Hodges' bandcamp store: Quake 1 and Quake 2.

They're also on Spotify. What I asked for however, was if there's a mod ready package for Darkplaces and KMQ2

I don't think so. If there was, it would be of questionable legality. I've seen a PSX Doom soundtrack package some time ago, but that one has the same problem. If there was such a package, we would not be allowed to post a link on GOG.

The bandcamp versions just have to be renamed; that should not be that hard, because the names of the tracks mention the corresponding level.