I stuck with the Quad 11Ls--and changed everything else! It sounds like your experience with the 11Ls, with different electronics, is pretty similar to mine.
The first thing I did was add a PS Audio A100, which was great, and I tried QED Silver Anniversary bi-wire cables. I also thought hard about a sub, but placement was a problem, and I decided that I was happy with monitors. I also decided that I didn't really want to move to separates, and got good deals on a Naim Nait 5i and CD5i, which I'd been interested in for awhile. So I sold the Music Hall stuff and the PS Audio (and went to DNM cables). I'm really happy with the setup now. I was immediately struck by how much better internet radio (streaming via a Squeezebox) sounds through the Nait, but the clincher was that mediocre recordings I hadn't been able to listen to at all (early Husker Du, for example) now sound great. Naim, at least at the low-end, doesn't do the transparency and soundstaging thing as well as the Music Hall/PS Audio combo, but it has me listening to a lot more music (and listening less to the gear).
In the end, I'm very satisfied with the 11Ls, especially with the current setup. They're fabulous speakers, and work extremely well in my less-than-ideal space (on a console eight inches from the wall). I think I'd have to spend considerably more to improve on them. Feeling settled at home leaves me free to tinker with my cheap office setup.