Jeff Rowland Preamps

IMHO, Jeff Rowland hit the sweet spot between musicality and transparency in the mid to late 90's with the Model 2/6/8/9 amplifiers. Earlier designs tended to be warmer, while later designs tended to be more transparent. The best JRDG preamp I've ever heard was a Coherence II, which I think also went back to the late 90's. As for preamps, well, though Jeff's designs are good for solid state, I don't know that I can listen to a solid state preamp anymore, I gotta have tubes in my preamp.
That's just my $0.02.

Previously used the Synergy IIi, and now the Corus. I like both preamplifiers a lot - both musical, low noise and fairly neutral. The Corus was a surprisingly step-up in detail, frequency extension and bass articulation.

Had the Synergy IIi for years and now the Criterion. Huge jump up in all the good stuff

i owned both a Consonance with Phono and later on a Consummate. i couldn't detect a really big difference between the two but enjoyed them very much. my bias for the Consonance is due to upgrading the line-stage module- a plug in box about the size of a pack of playing cards- for $450; the sound opened up considerably from that modest investment. the phono stage was quite good also and was fully adjustable for MM or MC with a variety of load settings.
the Consummate had one annoying drawback- the balanced input connectors didn't "lock" onto the cords- requiring the user to be careful when moving the preamp less your wires fall out. i got a lame response when i asked tech support at the company about this. but it did sound quite good as well (i checked to make sure it ALSO had the line stage upgrade).
i am quite sure Rowland didn't stop improving their line after that just to make me happy, but the lack of SE inputs on the Synergy plus the inability to upgrade from one to the next iteration made me think twice about that piece.
the Coherence-II was a very elegant component but needed a special battery-pack that petered out every few years. it didn't last very long in the market for any number of reasons- the batteries? too expensive to produce? technical issues?
well now we have the Corus and the Criterion, both VERY beautiful preamps and both VERY expensive. No longer are you looking at $5K-$8K to get a clean, full featured preamp from JRDG. this is still a huge amount of money and it won't get you even close (exception was a recent very-rare used Corus for sale). i won't say you shouldn't wait until you have the money for one of these pre's, but i can also say "look around" at Ayre, Pass, Levinson, etc. for a very quiet line stage.
OTOH, if someone would like to sell a "tiny-scratch near the back" Criterion to me for $12K i would have to bang my head against the wall for a couple of days thinking about it. right now i am using a Levinson 326S with Phono which i can
find little to complain about (other than the lack of a diamond-etched aircraft aluminum faceplate). and i am still waiting for someone to comment on the 725 Monoblocks due to go on sale "someday"...

"the Coherence-II was a very elegant component but needed a special battery-pack that petered out every few years. it didn't last very long in the market for any number of reasons- the batteries? too expensive to produce? technical issues?"

It was actually sold for four years, which is a respectable life span for a high-end component. And the comment demonstrates a misunderstanding of the batteries. The battery power supply requires a pair of Panasonic marine batteries. Rowland replaces them for about $100, plus shipping. I've had my Coherence II since the Spring of 2003 and averaged 5 years of use out of a set of batteries. Rowland replaced them the first time, and the second time I used my local guy - it was easy and cheap. The Coherence II has a few issues, but the batteries are not one of them. On the contrary, they're a big reason that the unit has such a low noise floor, which is critical for a top-shelf preamp.