@ David - thanks for your detailed report. I'm currently driving a pair of Paradigm Sig 8s (v3) with the VS-115 (w/ KT-120 power tubes). As mentioned, my pre is the Ref 5 SE, but it's still in its break in phase. Chris Osanna, the ARC tech manager, said it will take about 300 hours for upgraded Ref 5s to break in and I have a ways to go.
However, early reactions on the SE version are positive, but as Mitch said, I'm hanging in there. I'll come back later with a more detailed review after full break in. All I'll say at this point is there is a noticeable difference - more transparent, better imaging and definitely better low end timing and transient response. But, I'll be back in another 250 hours with more reactions.
As far as the Ref 150 is concerned, I appreciate member feedback especialy since the Ref 150 has been on the market for some time now and folks should be able to express more reliable impressions. So as I said above, I would be grateful to read more feedback.
The Ref 75 is obviously less expensive than the Ref 150. However, if and when I upgrade, I think I'll probably opt for the Ref 150. The S8s have some pretty rough capacitive phase angles and impedance curves in the low end. So I think the 1000 joule power supply in the Ref 150 may come in handy.
Of course, if the EE techie members think I'm mixing and matching apples and oranges with respect to power supply headroom stats and low end phase angles and impedance curves, clarification would be welcome. As an fyi, I supplement the super low end (50 Hz and below) with a sub woofer, so my impression is that I'm rockin' ok.
Thanks again guys.