Don't know if you've pulled the trigger, tswisla, but since I extensively A/Bed both at home, I thought I'd weigh in.
The bottom line is that, assuming cost is not an issue, I'm guessing most enthusiasts would prefer the INT -60 to the INT-30A.
The longer story is a bit more complex.
I had the 30 for a long time, and loved it: silky, sweet, musical, warm and romantic.
While the amps are pretty close, the 60 is not as romantic. I consider this a loss, but the 60 is longer in audiophile-y virtues: more detailed, precise, and revealing. Though still very musical. I expect to have it in my main system for many years.
The big difference is that the the 60 is far less limiting for speakers choices. I found the 30 to be less than ideal even for pretty efficient speakers, such as the 92db Montana EPSIIs, and even the 97db Vaughn Zinfindels (which have powered woofer). In fact, I blew several Fountek tweeters in the Vaughns, probably due clipping, and I'm not a super loud listener.
The 60 does not have that issue, and mates beautifully with my Daedalus Ulysses, even going pretty low, though the Ulysses are not especially noted for that.
So unless you're running really efficient speakers (my recollection is your Harbeths are not), I think the 60 is a better choice than the 30.
There is a substantial difference in cost, of course, and for better or worse, a good bit of that seems to reflect the much more luxurious casework in the 80.
As with all things Pass, very worth checking with Mark at Reno Hi-Fi. (I think he mostly concurs with my comparative assessment of the amps, btw.) He's a really nice and helpful guy, and will do his best to work with you.
Hope this helps.
Best,
John
