(1) Is using the internal receiver/prepro test tones good enough? Also, do the receiver manufacturers use a particluar db reference point? I think I read that B&K uses 75db. (2) Video Essentials uses 75db as a guide. Avia uses 85db. I own a copy of the Dolby Spectacular (V1) DVD. I believe it has speaker calibration tones as well. Does anyone know its reference point (75db, 85db)? (3) I plan on using two passive subs and an amp that does not have a volume control. Is the receiver/prepro sub level settings good enough? Or should I hook up a stereo preamp (in between the receiver's sub out and the sub amp) inorder to achieve volume control over the sub amp? I do have one in the closet, but is it necessary? And why? (4) If you think that I should use the preamp as a volume control, what volume setting should be my starting point? Thanks. Rich B.