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.