Recommend a Used Solid State Preamp for About $5k

Mitch, so you're replacing your Carver with the Pass(s)?

Honestly? I'd keep the ARC -- you'll have a wonderful SS/tube sonic balance, and besides, you won't find a used SS equivalent of the Ref2 mk2 in that price range (e.g. a used Levinson 32 is $10K +/_ with no phono!)

You'll have a really great system w/ the addition of the Pass(s) but the weak link (no disrespect) will be the Signal Cable stuff. With the new amps, you'll be able to hear the increased performance afforded by Purist Venustas (or even Musaeus), or mid-priced Siltechs, or Straightwire Virtuosos (these are all extremely neutral cables, perfect for the SS/tube combo you'll have.)

check out the Ayre K1x

Well, I can recommend the Ayre K-1XE.
It is also very well reviewed, as is your ARC Ref. 2.
(I have heard both, as my friend has the same ARC. I agree that the ARC is a good preamp too.)
I will not say that one is better than the other, merely different.

The Ayre is very quiet with no tube rushing (obviously!) and a very low noise floor. (That is what I like most about it.)
It also has optional built-in phono boards that are very good. (Much better than the old ARC PH-3 which I used to have.)
It has a remote, although it is very basic, in as that it only controls volume and mute, unlike the ARC remote which will give you more controls. (Personally, I don't need more, as I typically only run one source, my turntable.)
It has a good number of inputs, 3 RCA and 3 XLR, and is a fully balanced design.

Personally, I am not sure you should change to a SS preamp unless you really can't stand tube rushing.
(FYI: Eventually the tube rushing got to me, and I made the switch to SS. And yeah, my hearing is sensitive to that particular noise. Most people can hear past it with no problem.)
If you can live with the tube rushing, I would not bother, as you have a very good preamp as is. (BTW, my friend has done some tube rolling to reduce the tube rushing and his is now much quieter than it used to be, in case this is why you are thinking of making the switch.) Plus it is my opinion that having some tubes in your system chain at some point is always a good idea. (I have mine in my Lamm M2.1 amps.)

If you insist on trying a SS preamp, the Ayre is a good choice. There are a couple of Ayre K-1s for sale here on Audiogon. (Unfortunately, neither is fully updated to the K-1XE model. I recommend spending the $1500 or so to upgrade it if you get one, as it does help a bit. Plus the E upgrade increases the gain of the phono section by another 10 db, (up to 70 db) which helped me with my low output MC cartridges.)

Good Luck!