BS&T -
Mirror Image
I don't think this album is particularly well-regarded in the BS&T canon (almost the entire classic line-up had left before it was recorded), but I think it's a real hidden gem in the CBS quad catalog.
Stylistically, it's incredibly diverse. You definitely won't find "Spinning Wheel" or "Go Down Gamblin'" here. It starts off with an almost disco/soul-type number ("Tell Me That I'm Wrong"), and most of side two is fusion-y instrumental prog weirdness (the epic multi-part "Mirror Image" suite). New vocalists Jerry LaCroix (previously featured on Edgar Winter's
White Trash) and Jerry Fisher sound nothing like David Clayton-Thomas or even Al Kooper, but they're solid in their own right and there's some great interplay between them.
The quad mix is fantastic! The layout of the instruments is very similar to the Chicago quads: stereo drums, bass guitar, and vocals across the fronts, with different horn parts, backing vocals, synthesizers, and percussion isolated in the rear speakers. I'd also say it's quite a bit better than the BS&T self-titled album and greatest hits quad mixes, which in discrete form sound almost as if the four discrete channels were somehow blended together by accident.
I've said it before, but I think this title paired with the following album
New City (which also has an excellent quad mix, and features David Clayton-Thomas back on vocals) would make a killer D-V two-fer. But until that happens, both the SQ LP and Q8 are surprisingly good examples of their respective formats