I've wondered why I've found that using speaker level inputs on a sub frequently sound better to me than using the low level or sub inputs. In some cases, it's definitely been that the line-level source I was using couldn't run the two sets of interconnects well. When I used two pairs of interconnects on a benchmark dac1 or dac2, the quality of bass was definitely degraded. On the other hand, this problem isn't there when I have a bryston bp25 preamp between the benchmark and the power amps/subs. I recently bought a bryston bp26 so now I have two bryston preamps and two benchmark dacs in two systems. I hope to be able to do some meaningful comparisons at some point. Little kids keep me too busy for much audio hobby stuff.