PSB Synchrony One Speakers and Pass XA30.5 Amp

It seems like you are listening in a near-field setup, so room acoustics may not have an effect. Make sure the speakers are at least 3 ft. from front wall and play with distance from side walls. I needed speakers to be 7 to 8 ft. apart and toed-in.

Are you getting 3D imaging and wide soundstaging? You should be with that amp.
Lastly, what are your speaker cables?

Did the PSBs ever have the vitality you want, driven by any other amp?  If so you know they can do it,.  Now you have to decide whether you want to design the rest of system to get that out of them.  I went through that with some Focal Electras and was quite happy with the result.  It literally to years of trial and error to get there  though.  If you haven't heard them do it in another system then I would ditch the PSBs, and go on the "perfect speaker" hunt.  The bane of all audiophiles known to take down even the high and mighty.

I agree that the XA-30.5 may not be the perfect amp for those PSB speakers. However, there are other factors at play. Pass Labs gear tends to be warm and musical, so combining a Pass preamp with a Pass amp may be too much warmth and not enough detail.
Many Pass amp owners use an ARC preamp, like myself. The ARC provides a bit of speed and resolution to the musicality of the Pass amp.

That said, I'm still not sure that the XA-30.5 is enough power to drive your speakers. My room is 24 (L) X 15 (W) X 9 (H), my speakers (90 dB, 5 ohms) are a bit more efficient than yours ( 88 dB, 4 ohms), and I am running XA-100.5's, which provide plenty of power. 
If you seek greater liveliness, it could be an amp/speaker mismatch, in which case I would change the speakers, or it could be that you need a preamp with a little bit more life.

mechans brings up a good point. Have the speakers ever had this "liveliness" that you are looking for? The speakers may benefit from more power, but I find it hard to believe the XA30.5 is solely responsible for the issue. Stereophile's review on the amp measured 130 watts before clipping into 8 ohms, 195 watts into 4 ohms, and over 330 watts into 2 ohms. This is a beastly 30 watt amp. Have you considered there could be an issue elsewhere? Would you care to list your entire system? What is the source? Sometimes power conditioners can make a system sound dull. Are you using one?