Preamps better than Parasound JC-2 ?

So I am assuming that it uses 2 x 6SN7GT and 2 x 12AU7 tubes?

Yes. It also has a fully balanced circuit internally.

While I am a bit considering tubes, that preamp has tons of tubes in it. The Backer Lab Rhumba is something I can consider, since it has 2 tubes and their access is also easy.

@milpai Just a correction of fact, if you get the MP-3 as a line stage only, (like the Rhumba, which isn't balanced), then it has only 4 tubes total. The remaining tubes you are thinking about are for the optional phono section.

@milpai 

Hum is not an issue of tube preamps any more than it is solid state. Hum can be caused by a variety of issues- ground loops amongst them, but I suspect its not that in this particular case.
There's no point in keeping a tube preamp on all the time like solid state. They should get to where they are going in 2-3 hours, unlike solid state which might take a week of on time.

In the case of the Rhumba, its output is actually single ended- its XLR connection is there for convenience only (this can be seen in the interior photos). This is why this unit hummed in the review you linked- the XLR cable the guy was using was picking up noise because it was running single-ended!

We make tube preamps with XLR inputs and outputs, and they are in fact actually fully differential and balanced all the way through- and (like the Rhumba) one stage of gain in the line section and zero feedback, and with a low enough output impedance to drive any amp made. So there are alternatives- BAT would be another.
Even if you were to go single-ended though, I still think you will find that the tube preamps have an advantage.

Seriously, just try a tube preamp, and see if you still want to play with solid state. You may find that to get similar or better sound, a tube preamp is less expensive.

I have never had any experience with tubes. So never investigated into tubes. I am worried that when a tube goes bad, it might cause some damage to the system. Besides tube rolling is expensive and I have no experience biasing the tubes.What are your preamp suggestions on balanced tube amps in the $3-$4k range? Will they be compatible with the Parasound A21 amp?

Its unlikely that a bad tube would damage the system or tubes simply would not still be around :)
You don't need to 'roll tubes' to hear tube sound although some collector tubes are pretty nice. I stay away from that stuff myself and it does not seem to hurt.
I'm not sure what you can find at that price- does it need to be new? If not, ARC, BAT, Atma-Sphere (disclaimer, I am associated with Atma-Sphere), Shiit, and a pile more I'm not remembering off hand.

Any particular reason you can't do with tubes?
There are some excellent balanced tube preamps available.