Hi, I'm looking to bi-amp the woofer section my NHT 2.5i speakers with a power amp. However, to ensure that the woofer section matches my tweeter and midrange, I need to be able to control or vary the amount of juice that gets fed to the woofer. I know some power amps allow you to adjust the amount of gain, level, or volume (e.g. a Crown professional power amp allows you to do that, however the fan noise is distracting for home use or the bulky NHT SA-2). What brands or models of power amps have that capability?