Monitors for Pass Labs 60 INT

I think you should consider the Wilson Benesch speakers. No relation to seller, but there is a pair of Discovery for sale on Audiogon at a good price. About 88 db efficient and should be a good match.

Haven't seen Sonus Faber mentioned. Some great used available plus newer monitors. 

Sorry. Just saw them mentioned. 

Udisa my experience with them has been at 3 separate shows and each time they made a big impression on me.  They are on the side of accurate, revealing, and big sound, so your Pass (which is believe is slightly warm) might be a great fit.  Amplification I heard behind them was lower powered tubes - I cannot remember the particulars but they were in the room with Devores Orangutan speakers and Leban integrated amps which are highly efficient and low power, respectively.  There were no big power amps present.

I would look at Penaudio Cenya Signature. I have heard them with the Pass 30.8 and 60.8 and was stunned how good the combination sounded. Stein Music also mated nicely but at a considerable price increase.