Volume Control-Power Amp-Subwoofer

This is probably a strange question-
I have a NHT subwoofer that came with the separate integrated amplifer. I was wondering how I could use spare power amps with more power in its place. Would I have to buy a separate preamp? I could route it through my stereo preamp or home theatre receiver, but would not have the separate volume control I have now with the NAD amp. Is there a cheap (I mean really cheap:) way of doing what I want to do? The power amps are Marantz mono blocks and only have an on off switch so I would need something.
I had the same problem and I have two ways to solve your problem. I have a stereo/mono amp that I use with a crossover on my sub and sounds nice. Most crossovers have a volume control on them, as mine does. I also have an extra Sony 55ES stereo 100 watts and 200 watts mono amp that has a volume control on the amp. You won't need a pre if you go with an amp like the Sony that has a built in volume control. Either way you go amp or crossover a class A/B amp will kill your class G NHT amp. I also had a NHT sub amp and found that both A/B amps sounded much better than the muddy sounding NHT amp. I hope this helps.
Thanks Jab that does help. Now I will research crossovers. I have two mono blocks that I want to bridge and use for power if I can. From what I understand, I have to make sure the subs impedance isn't too low for the bridged amps.