The Unleash does do that, and can bump your power output up to as much as 100 watts if you want. I have one, and it does work very well. Of course, everyone hears these things differently, and some people will never like the sound of an attenuator and/or external power amp, even they're imagining the difference! Basically though, the Unleash works very well and does what you're looking for.
Another option, which I did before the unleash, is to use the line out from another attenuator, and from there through effects and to a solid state power amp. It's basically the same thing, but the Unleash is rather more elegant, all being in one box.