Pass labs XO.2 or Janus tube pre-amp.

Is any one on the great audiogon forum able to tell me if going to a tube pre amp like the Janus tube preamp an up grade in sonics?
I have the pass labs xo.2 with X 350.5 and want to try a balanced tube preamp with a great phono stage, just do not want to give up much bass sound.
Any comments would be helpful.
There are no janus preamp stores here in Denver, Colorado.
You will need to find out what the output impedance of the Janus pre is spec'ed at. Some tube pres have a fairly high one and Pass amps have a relatively low input impedance. You would want the input impedance of an amp to be 10 times greater (or more, general rule) than the preamps spec.

Right now I am listening to a Conrad Johnson tube pre going into a Pass XA30.5 with excellent results. The CJ (a CT-5) has an output of 800 ohms and the Pass's rca input is close to 20k (I have to use the rca's) so I'm at a 25 to 1 ratio.

Chances are good that you will be fine unless the Janus output is abnormally high.
Matching the Pass with a tubed preamp is a good idea. Like you said, you don't want to give-up the bass, and you probably don't want to give up that silent background. Some tube preamps will really enhance the midrange and 3-dimensional aspect at the detriment of the first two.

It's really best to arrange for a demo, or buy a piece of equipment with good value and resale. Matching amps and preamps from different companies can be rewarding, but also a little risky.

The BAT fits that role for me. It gives-up a tiny bit on the bass c/w running direct, but it is far more satisfying overall. I'm not sure how good their phono section would be.

Another option to consider would be a move to the XA.5 series.