The compression induced by the tube pre is really obvious there, sounds much smoother and more polished than the solid state pre you used.

As for noise there’s not much you can do, you should however remember that low frequency tracks (like bass guitar) will always sound noisier than others as there simply is nothing much but noise higher up in the spectrum. In my experience all you need to do to mask this is have a high-mid track, be it vocal, guitar, cello, anything in that range, play simultaniously.

Here’s an example; http://dl.dropbox.com/u/14392951/In_the_Middle_of_the_Night.mp3

Loads of noise in the first bar when it’s just bass (it’s one of my tracks so I’m allowed to slag it off xD) but when other instruments come in at the start of the second bar; guitar, synth and BVs, the noise is barely noticable. By bar 4 when the drums come in you wouldn’t be able to tell there’s any noise there at all! And remember, those other tracks contain just as much noise! I used the same microphone and the same pre for all of the tracks, and all instruments are played through the same amp. With the obvious exception of the drums, which are sequenced, because 1-mic drum takes rarely go well.