Pro-ject tubebox ii : muffled sound

I found a Tubebox ii at a thrift store for a price that I could not refuse.

The sound is muffled, like it is so warm it is in the next room. It still has the original tubes -- is this something that a new set of tubes will likely fix up, or do I need to take it in?

To that end, it calls for 12AX7A tubes, and I'd love any input on choosing replacements (I'm new o tubes) -- the price range and lack of adequate descriptions for tubes is befuddling, but I assume the differences are significant. I can spend anywhere $20 to $2500... hmm.. it'd be nice if the $20 pair worked..

I've been using my McIntosh MA6500's built in phono stage for about a year, and have been happy enough with that.
The sound is muffled, like it is so warm it is in the next room
Could you explain this a little better please? I'm having a hard time figuring out just what you mean.
I'll try.. At first, I noticed the sound was quieter than my standard (internal SS phonostage) setup, so I turned up the volume, at which time I noticed the warmth of the sound -- highs and lows cut, mids emphasized -- this was all in a few seconds. Once vocals came on it was clear that the sound was not right -- like it was in the next room, muffled, weak sound, loss of detail-- in short: bad.
Okay, I think I catch what you mean now. I've never heard the term "warm" used in that context.
Perhaps that's why it was sold at a thrift store and not Audiogon?
Does the Tubebox have switches on the bottom for cartridge matching? Check them to see if they are in the right position.

Then I'd try those $20 tubes, see how you like them and then decide if you want to upgrade.

new tubes ((just went with Sovtek) did, in fact, bring this thing online. yay thriftstore!