Thanks Jtimothya. Well, can't exactly say I know what the RF 2 (SE) sounds like because I've never done a serious listen to the RF 2 (SE or non-SE versions). Having said that, I do know something about the Ref 3, Ref 5 and Ref 5 SE linestages, having owned all three at one time or another.
Frankly, I wasn't bowed-over when I switched out the Ref 3 for the Ref 5. However, I think the SE version of the Ref 5 was an improvement. I surmise the same would be the case between the Ref Phone 2 and the upgraded SE version.
The SE versions of the Ref 5 and Ref Phono 2 incorporate improved Teflon coupling caps, a doubling of the power supply and several other circuit and component changes. IMO, the Ref 5 SE is a better sounding pre as compared to the non-SE version. As stated, I suspect the RF 2 SE shares the same sonic improvements as its sibling.
Based on experiences with various ARC components, if I had to make a knee-jerk guess about the PH-6 and PH-7, I would take shot at the PH-7. IMO, it's a champ.