Quad ESL57's (the original Quads) with a sub woofer weren't any good for stereo?

If I had ESL57's and a sub I would replace the HT receiver and keep the Quad's.

Usually when a surround system doesn't cut it the receiver is the culprit. Most HT receivers don't do a very good job with two channel stereo.

If you like your current system adding a good sub woofer would give the biggest bang for the buck. REL makes very good sub woofers.

in their very good articulation in the midrange, they should be the start of a good two channel system. Indeed, they do not dig very deep, and deal with sub-40Hz material with harmonics and psychoacoustic effects alone. Hence, adding a good musical subwoofer like the Rythmik F12 (or a pair) would do wonders for your listening experience. There is an extra output on the 8000Q which could feed the subwoofer. Run the Ruarks full range and try crossing the Rythmik over at 40Hz. You might have to play with it from there.

My assessment?

Rythmik subwoofer!