More watts or better power ?

If I read your OP correctly your sole reason for asking is that the rated amp power is at the low end of the recommended range for your speakers.  Sorry…forget that and just enjoy the music.  You have an excellent system, well chosen to provide a quality listening experience in your small bedroom.  And yes, if you have to tinker, get some high quality jacketed CL rated speaker wire.  Transparent HP122 or similar.  You’ll have to crimp and solder terminals after you pull it through the basement though.

Get a much larger amp and sell the XA25 to me.

I would think a larger size amp would be like buying a new car and opting for the model with greater HP.  A larger size amp would work les hard and I wonder if this in turn would produce better sound.  I have always thought the larger the amp the better.  However, it would have to have the type of sound you are trying to obtain.

Not sure if you have a pair of subwoofers.  When I added my REL S2 subs, I was able to reproduce more bass at lower listening volumes.

There’s been lots written but here are my two adds: one more factual guidance, the other my opinion based on hearing various Sonus Fabers.

1. re: power vs quality - more power is only beneficial if you are exceeding the VOLTAGE limit of the amp. The Pass labs stuff can deliver plenty of current for its modest voltage (about 14 volts rms) under normal dynamic conditions (where one uses on average ~ 10-% of rated power due to music’s peak: average ratio) . If you are beginning to clip - get more power. Else. move on IMO. Note my answer assumes that money is limited and you can only spend your budget once: so money spent on an amp, for instance, is not spent on speakers.  Hint: i think you ought to look at speakers - whether i be subwoofers or a thoroughly different speaker. Yet that may not match your personal likes.

2. re: the speakers - it would be helpful to know the problem you are trying to solve. They will never have much bass - the laws of [physics are not on thier side, yet many speakers that solve that problem violate the laws of decorating. Only you know.

That said, when i have heard the Sonus Fabers they always sound somewhat bright and harsh from the upper mids up. This is, IMO, common in many components that seek "detail". It does not sound like music to me. Don;t get me wrong, they are very good speakers, but IMO nowhere near the quality of your preamp and amp (having only heard *ABOUT* the BHK, but knowing Nelson’s stuff).

Yet that may no be your objective at all. Step #1 if finding a solution is knowing the problem!

G

Audiophilia nervosa? We all have it.
Powered subwoofers and external crossovers to reduce the bass load on the Amators might be worth trying.
You have great stuff, by the way.
Have fun!