ProAc 1SC's would be a match made in *heaven* with that amp. The ProAc's LOVE tubes, and present a very agreeable, easy load on a lower-powered tube amp.
They don't show up used all that often, but when they do, they can be had in your price range (depending on what finish you want).
I ran mine with a Cary SLA-70 (35 wpc) and then moved up to the ProAc 2S's when I moved into a bigger place and the 1SC's sounded too 'small' for the new room.
Someone just listed a pair of black 1SC's in the last day or so (not me - and no affiliation with seller). Check 'em out, and Google will pull up a lot of good info on them if you're interested.
Oh, and they like to be on tall, sturdy stands (24-28 inches).