All the Rogue monoblocks's 120's 150s' and 180's have a very high input impedance and very high gain, they are a great match for a passive preamps and do not need any active preamplification at all.
You may even have the problem of them being already too loud at 9 o'clock volume with an active preamp, because of the amount of gain the 180's have.
Try this first for just $49 and save a stack of money and potentially have a more transparent sound than any active preamp can give.
[url]http://schiit.com/products/sys[/url]
Cheers George