New speakers but old Rotel Amp

+1 for the Benchmark AHB2. a remarkable amp!

You can easily tweak / modify / damp the chassis of the RB981, eliminate the ringing of the internal heat sinks, replace the stock power cord ( I am aware it is not a removable cord ) with a quality, heavier gauge cord, change the feet, upgrade fuses, etc. If you are not familiar with doing any of this, or are afraid of opening it up, I can help you. MrD.

suggest you stick with a good sounding (better than rotel) class a/ab solid state amp, especially since you have tubes in the linestage already

harbeths (and esp. the monitor 30) can, imho, use good bass control that most lower cost tube amps have trouble with

many out there to choose from, but i suggest considering:

hegel
pass
ayre
luxman
mccormack

I would go with the Prima Luna Evo 400 amp. Synergy is the key to a great sounding system. 

I read Herb R's Review on the previous Harbeth 30.2s. He liked the Pass, but it appears that he preferred the PrimaLuna and more, but it's kind of hard for mo to decode the end of the review– what does his "But" and the following other "But" mean to me since I equally love to listen to the music in the background, engage with the music with my ears and play along with my guitar, and listen to the music in its entirety. I listened to Riders on the Storm three times. The first time was just hearing it while I was in the room, the second time I was seated, focused, and really listened to the song, and the third time was sitting and listening to the instruments. Right now I'm listening to a lot of Aaron Copland's music, pieces I heard Mr. Copland play on my grandmother's Steinway with my grandfather In their house as a kid. I can still see and hear it, he was such a nice man. Too bad I was too young to appreciate it to the extent I do now.