Hi there,
In another thread you asked me about RBI vs. SVP-Pro so I thought I'd answer here in your own thread.
Anyway: considering the fact that you want clean tone with a minimum of hum and hiss, I would definitely recommend the RBI over the SVP-Pro. As mentioned I now own both. I do like the SVP-Pro a lot, partly for its warmth and smooth overdrive, and especially for its versatile tone-sculpting ability (and I don't even use the graphic EQ). However it would not be my preamp of choice if I wanted clean quiet tone! My SVP was retubed by its previous owner and noise is not a major factor but some hiss is still there. Also, I have to be very careful with EQ and gain settings if I want clean tone from my SVP. Now, that might just be because of the particular tubes I have in mine, but IMO the reason many bassists use the SVP-Pro is because it sounds so good when it's unclean (so to speak).
My RBI, on the other hand, is *amazingly* quiet! I typically keep the Drive control at 40% for subtle tube dirt, but by turning Drive off all the way and being careful with the Presence control, you should be able to get clean tones. The RBI does have an inherent mid scoop (which isn't counteracted by the Midrange control), but keeping the Blend control at 40 or 50% makes this a very subtle factor. You could also turn the Blend control all the way off: if I'm not mistaken, when this is done the treble, bass, and midrange controls will still be active but the tube emulation will be bypassed along with the Drive and Presence controls. In other words, turning Blend off should allow for especially clean tones. In addition to all that, there's a bypass switch so that *all* RBI functionality will be bypassed (including EQ).
I hope this helps... good luck in your search.