I am about to pull the trigger on a SVS 20-39V CS+ sub which needs external amplification. The SVS site states that with an external amp you have no level control, auto ON-OFF, etc, which is fine with me. but the site also mentions that there is no phase control. I have always used this feature with the powered suv that I now own and have always noticed more bass in one possition over the other. Is the auto-phase situation mute with an external amp and a passive sub?