I've been using the Crown XTi 2000 for a few months now. Input sensitivity is significantly lower than the Stewart World 2.1 and Crest Ca9 amps I'd been using, but my SansAmp RBI has no trouble pushing it.
I am interested in how you would contrast and compare the three amps that you mention. I own an RBI, a CA9 and a Stewart World 2.1, so I know how those two amps perform with an RBI as the preamp.
IME, while both the Stewart and Crest perform well, I must agree with those who favor the lead sled. The bass just hits me in the chest and punches more, at any volume through the Crest. And this isn't just a quality that can be EQed up to sound the same on the Stewart. All the cabs I have played through using these two amps (Acme B4, BagEnd 4x10, trace elliot 15) sound better to me, powered by the Crest.
How would you rate the Crown, by comparison with the Crest and the Stewart?