Well, after waiting a couple of months to get my Bruce Moore Custom 120's back, they've finally returned and now have new matched quads of EH 6550's. They sound terrific. Great definition, and bass that sound very satisfying. Still, I had my IRD 100watt mono blocks sitting around, so I got a couple of inline 50 Hz low pass filters and connected them to the sub input. The difference in wattage between my tubes and the sub amps may be responsible for the somewhat underwhelming difference. The speakers sound larger, and bass definition is sharper, but overall, there's not a lot of difference, maybe 5-10%. That's what you want to hear though, right? The Gallos as is, without the need for bi-amping, are pretty special. Of course, when the, what are they, 220 watt per channel, sub amps come out with their ability to tailor the power and frequency more specifically, they should make a more significant difference. Still, it's kind of fun to have a little added bass thrown in.