You don"t want to use the high pass filter on the A370PEQ, it's not very good. For low level (RCA) and speaker level inputs I prefer the A370PEQ3. This model has two line level inputs but no output. The XLR3 is the way to go if you have balanced outputs on your preamp. However, as you noted, it doesn't have speaker level inputs. Base your choice on the type of input you need.