More watts or better power ?

I'd vote for better dac and or nice silver interconnects. They will allow you to really see the potential in the bigger components, in my opinion. 

Mark that hi-fi rig is impressive. I’ve never heard PS Audio BHK in person but many recommend very highly and the designer is something of an audio legend I understand?

50 watts of tube power can be a lot with big power supplies storing massive joules of energy.

Your front end components / amps are excellent, and you have a very good DAC in the Schitt Yggdrisil.

You ask, what would be a better investment (most bang for the buck) into the system as it is now, considering being in the bedroom of a small house. You suggest replacing the XA25 with a higher watt amp, or a power conditioner (PS Audio Power Plant II?) Or possibly upgrade the Minima Amator (which are sounding very good) to another set of speakers.

You said the speakers sound very good. What is the sound, as it is, lacking? What do you wish it had more of?

do you feel your power is dirty? If not then investing in small footprint full range speakers instead of a conditioner would probably be a better investment. If they are 88db - 90db efficient for the smaller space 50watts should drive those will no problems at all. As it is a bedroom that may be smaller, then mini-monitors are more practical of course. If your speaker cables and interconnects are sounding good I see not reason to spend the extra dollars there yet. Although i have found the right speaker wires and interconnects to help improve detail retrieval and create a bigger more balanced sound.

More power definitely, NO question.

The Pass amp is way more powerful than its rating. It is 25 watts class A but it then switches to class AB and is good for over 70 watts.

We need to get some facts straight here… the XA25 shoots WAY above its ratings, as is typical of Pass Class A amps. The class a’s run very high biased mostly pure class A to the clipping point. Here are the actual measurements for that amp…

“Pass Labs specifies the XA25's output power as 25Wpc into 8 ohms and 50Wpc into 4 ohms (both equivalent to 14dBW). However, as you can see in figs. 4 and 5, the amplifier exceeded its specified power output at the clipping point, which we define as when the THD+noise equals 1%. At that THD+N percentage the XA25 delivered 80Wpc into 8 ohms (19dBW) and 130Wpc into 4 ohms (18.1dBW). It appears from the shape of the traces in these graphs that Pass specifies the XA25's power as when the THD+N is close to 0.01%”

The amp is not an issue with your speakers. Look into other areas, cables, room, placement etc, as others have mentioned.