got a chance to spend a couple hours with the cryo reflektors w/ my th600. can't give any definitive since the sound may change but early impressions are as follows.
if the stocks are mid centric and the eh are more u shaped i would put the cryo reflektors somewhere between. they are smoother than the EH but more detailed than stock.
for specifically the th600's sig i think its the best of the three. sometimes the EH can be fatiguing for me with its hyper detail. the cryo reflektors give a good in between for easy long listening sessions.
EH has more wow factor and better with instrumental music/active listening, cryos for a smooth session.
will report if that changes.
The cryo Reflektors just keep getting better. I've got about 10 hours on them and what I notice is extended and tighter bass and deeper soundstage. I seem to be listening at lower volume on some tracks with no loss in sq. They are slightly less transparent than the EH, mostly on the high end. These tubes are a very nice change of pace - and I agree they are less fatiguing!