Thanks Gentlemen,
A note of clarification (if helpful): I do have a separate amplifier for the subwoofer. It is a typical amp not having volume controls (not an integrated amp).
As an alternative solution: I do have a decent to good Onkyo receiver that is not currently being used. It could be the subwoofer amp. Would putting the receiver inline from the preamp via a line level be a good or better solution (not in how "good" a subwoofer amp the receiver may or may not be compared to my current amplifier - probably even trade) but as a solution compared to attenuating.