So, I've been thinking about getting a SansAmp, because I only hear good things about them. I know that Geddy Lee uses an RPM, and I love his tone, of course, but I was reading on the Tech 21 website that the RPM can be partnered with the RBI. Both are preamps, I don't really understand why you'd use them together, for bass at least. So, my question basically is, which one would you guys recommend, why would you want to partner them, and do they both do effectively the same thing? There's a drive knob and a couple mid knobs on the RPM...seems like you could get a really ballsy tone there. Thoughts? Thanks in advance!