I was originally going to purchase a Outlaw 7125 along with a Marantz 8801 preamp but I am now thinking about a Outlaw 7500. My concern is this.
The Outlaw 7500 has a input sensitivity of 1.43v while the Marantz 8801 has an rca output voltage of 1.2v. My understanding is that preamp output voltage should always be larger than amp input sensitivity for the amp to be capable of full rated output.
In comparison, the input sensitivity of the Outlaw 7125 is 1.0v and is less than the Marantz 8801 1.2v output voltage.
My speakers are Von Schweikert VR-33 towers (8 ohm sensitivity 90 db) and 3 LCR-2 for center and surround (4 ohm sensitivity 88db).
Ah which one, 7125 or 7500?

Either one will power your system to ear splitting levels. If you routinely take your system to full output you won't be able to hear the difference anyway because of hearing damage. I have both amps and the 7125 is a real beast for power but the 7500 is what I use to drive my Magnepans since they need a bit of power to sound their best. Also there just isn't a big difference in available SPL from the two amps. The 7500 has about a 2 db advantage at full power. You are right that the 7500 won't be driven to full output by the 8801 whereas the 7125 will be driven quite well to full output. Doing the math it would appear the 7125 would get a 20% overdrive for an equivalent power of 150 watts and the 7500 would be underdriven by about 16% for an equivalent about of just under 170 watts. The biggest advantage for the 7125 is the two extra channels. Since you may not use them, the transformer has a lot more headroom available for the five used channels and allows more flexibility for future additions to the system. Bear in mind also, that the mains could be bi-amped using the extra channels which would give them almost 300 watts available. The remaining channels don't need anywhere near the power from the 7125. I would save the money and get the 7125. Test it in your system and if it doesn't make it you can return it and get the 7500.

Thanks for the reply.