Monitors for Pass Labs 60 INT

Udisa:
Size wise M30 not too bad,even own bigger C7 on my small room,mine 10x9 similar to yours.
Been driving them with tube at 80w ,enough power!
Been own pass labs INT-150 ,yours pass will drive harbeth with easy.
Is size matter maybe I've try the P3 ,smaller in harbeth line.
You can see my set up on system,mine can only take from angle side cause I can't take from front cause too close about 6'.

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.