Published gain of the Pass X2.5, X1

.
Quoting the X2.5 manual:

"The gain control toggles between two settings, offset from one another by 10 dB. The up pointing arrow selects +14 dB and the down pointing arrow selects +4 dB. When used with our own X series power amplifiers, which are quite high gain (30 dB), we find the +4 dB setting to be most satisfying. With other product we suggest that you let your ears determine which setting conveys the most sonic benefit."

and:

"Gain, Balanced = selectable 4 dB or 14 dB output
Gain, Single-ended = selectable 4 dB or 14 dB output"

So, you have the SAME adjustability thru this preamp irregardless of the connection type used. This allows you to tailor the sound and attenuation characteristics based on the your accompanying equipment's gain requirements.

As Pass describes above, the lower +4db setting would be beneficial if you use the balanced connections of this preamp with a high-gain amp, allowing a larger, finer range of volume control and - from what I have heard - a less forward mid-range presentation. But in any case, the appropriate choice of settings is also affected by the gain of your amp, the incoming signal strength of your source and the efficiency of your speakers.

Remember - this is all about gain stages, input/output impedance and whether or not you use true balanced or single-ended connections.

-- IN OTHER WORDS -- it is VERY system/component dependent!!

I hope that helps.

Forgot to add-

This preamp uses class A gain stages throughout, again irregardless of input/output type.

This is a fully-balanced design, so S-E input signals are converted to balanced internally to allow the common mode noise reduction circuit to benefit even unbalanced signals. However, there are still definite advantages to using fully-balanced connections both in and out with Pass stuff.

If you have further questions, you may want to call Pass Labs themselves. They are exceedingly customer-friendly and open to these types of questions.

I currently own Pass X-250 & X-3 amps, and will be receiving a new Pass X2.5 preamp tomorrow, actually.

I too have considered tubes in a preamp, but have decided to remain on the fully-balanced SS side since I am already there with the Pass amps, just for system synergy sake along with the points made above (impedance matching, gain settings, etc).

I don't know if all that really matters in the grand scheme, but I have no chance to audition comparable products in-home, so I try to avoid gambling too radically by using educated guesses gleaned from research of online reviews and conversations like this one. It's still a crap-shoot, as everyone hears things differently, but that's when you start to appreciate the Black Art that is involved in this horribly finicky (and expensive) hi-end audio world!

Sorry I couldn't give you any comparisons.