I had the opportunity to trial a REL G1 sub with my Avalon Eidolon Diamonds. This may sound strange to Avalon Eidolon owners but in my upstairs room, for some reason I get a significant drop off in bass response below 40 Hz with only a slight increase between 20-25Hz. I used one REL G1 and hooked it up directly off the speaker terminals on the amp using the Neutrick cable. I set my slope on the sub at 30Hz and set the volume at 20 (the G1 comes with a great remote that you can dial in the bass response from the listening chair). It mated seemlessly and its driver is equally as fast as the woofers on the Eidolons.
I would not hesitate to try a sub with full range speakers. It can open up the soundstage even more and improve low level detail and imaging. Plus it can give that visceral bass response some may crave. One caveat though is that to get a great response like I experienced, I'm betting you have to spend $$ for the sub. The REL G1 ain't cheap, but it can potentially change the sound of a system dramatically for the money spent.
I would not hesitate to try a sub with full range speakers. It can open up the soundstage even more and improve low level detail and imaging. Plus it can give that visceral bass response some may crave. One caveat though is that to get a great response like I experienced, I'm betting you have to spend $$ for the sub. The REL G1 ain't cheap, but it can potentially change the sound of a system dramatically for the money spent.