Quad 12L Actives & REL Q108 Sub

In response to your sub setup question even though I have never heard the Quads I don't think the speaker brand matters. Some things I've encountered with my Rel. For me I have the crossover set to just below the low limit of my speakers. The low limit on my speakers 45hz and have them crossed over at 43hz. You don't want to hear the sub from any 1 area. The phasing for me was the tough one. Rel only gives you a choice of 0 or 180 degrees. That means you have to move the sub to really fine tune the phasing. I had the placement off by 5". Last get rid of the stock cable. In a million years I couldn't believe that the cable makes a difference but for me it was instantly more attack and decay. So in summary for me the phasing was the hardest and longest to get dialed in correctly. For almost 2 years I had it wrong (the phasing) and thought my Rel B3 could not keep up with Dyn C1's. Well I was wrong - the Rel integrates really good but not just a simple setup.