I received my XA 25 last Friday. It is twice as big and twice as heavy as the Aegir. The amp came in a large single box surrounded by expanded foam. The amp is heavy at 45 lbs vs 22 for the Aegir. The XA25 is rated at 25W but will put out 80W if needed. The Aegir is rated at 20W and will put out 28W if needed(per Stereophile bench test. I have subs so the main amp is driving my Crites Cornscala from 100 Hz on up.
As the XA25 warmed up I would say it never gets above 120F. The Aegir also runs warm. The XA25 will pull 240W just sitting there without music. The Aegir has a standby switch and a light that stays on. The Pass powers on immediately without a relay clicking. It is fused and I don't believe the Aegir has a fuse.
I am using ribbon speaker cables with spades on each end. The speaker connections for the Aegir were good and could not be over tightened. The XA25 has Furatech connectors which I was able to insert the spades through the bottom. It holds the cables quite securely.
I started listening I immediately noticed better vocals. They just sounded smooth. This and the percussion instruments simply sound right. Brushed cymbals, background percussion played softly are easily audible and very easy to listen to. Midrange in general is improved. I found myself listening for longer times without fatigue. I must admit it is quite easy to play at loud volumes with my speakers. I was told they are "around 100 dB efficient". If I turned up the Aegir too loud it would go to protection. Try as I might I don't think I could even get the Pass to sound stressed. I had to cry uncle and turn it down. My typical listening levels are 85-95 dB.
I believe the soundstage is equal to the Aegir but even more fine detail. Bear in mind the Aegir was good at this as well. If listening to electronic music sounds can start at one channel and go all the way across the sound stage without gaps. I listened to every kind of music I could think of and some good and badly produced albums. With each amp it is easy to find mistakes in production but the XA25 kind of smoothed things over.
So in conclusion, the Aegir is a fine amp. The XA25 lists for 6X as much. Is it 6X better? We all know that doesn't equate, but it is worth the money. The Crites speakers may seem forward to some with a slightly hot tweeter. The XA25 is a perfect match.
PS. Forgive me since review writing is not my profession.