Unfortunately I cannot compare the XA25 to the XA 30.8 as I own the XA25 and never heard the 30.8.
As others have mentioned, the XA25 is a “different” Pass amp and not just in that the 30.8 has balanced inputs and the XA25 does not. From everything I have read (and is represented in the quoted article above), the XA25 is designed differently with different design goals in mind. I am not an EE, but I did try reading through the quite long diyaudio thread about the XA25 and it clearly kept many folks guessing on the design - even with Nelson’s occasional and sometimes humorous prodding.
I will also say that it is not your average 25 watt amp. I use it with my Dynaudio Heritage Specials, which are not that efficient, and in my space and at the levels I listen at - definitely not arena rock, but occasionally a bit louder than moderate - I have never felt that the XA25 was underpowered. Just my opinion of course and I know some others have felt that the HS speakers did respond better with more watts, but I am incredibly impressed with the XA25 and HS combo.
As for reliability, Pass products are built incredibly well and with reliability as a first feature.