Swapping W4S to Pass Labs XA- worth it?

Tell us what the Pass would have to do that your current amp doesn't do that to you would make it worth the change?  I imagine they will sound slightly different, but without knowing you goals, or even the rest of your system, it's hard for anyone to say whether changing will be a good decision.

It really appears strange that you seem to want to run the Pass amp in A/B mode.

Stereophile measurements of 30.5 shows quite different numbers then 1% at 30 watts, in fact extremely different. I think 1% is at clipping when in AB. Here are those charts. https://www.stereophile.com/images/archivesart/509Pasfig4.jpg

I am not "planning to run it in AB mode", I just want to ake sure it does not clip in HT mode. I never listen to stereo at very loud volume.
As far a goal - I may be like more "liquid" presentation of some music, which in my case is small ensemble modern classical music, opera, small jazz ensembles and jazz vocals, and classic progressive rock.

For stereo listening I am planning directly feeding amp from AYON CD-5.

Well, I decided to pull a trigger on used 30.5 (late build, less then 2 years old). 30.8 is simply too big for my rack and will stick out too far. Will report results when all received and set up )))

PS I am not using preamp, instead I am switching amp inputs via Rolls SS32 switch, a very well build simple device

Hello Michealkuz, 
Congratulations on getting this amplifier and I believe that you'll be very happy with your decision.  Given your (stereo) listening volume habits and music genre  I doubt  you'll use more than a few watts (the majority of your listeniing) and will rarely move out of class A operation. Let us know your listening impressions. 
Charles