Have a look on http://www.usedhifishop.co.uk
. They recently had some nice bargains on the go including a Creek CAS4040 (£40) and a seconhand MF (£125)
Looking forward to collect a Creek like that one myself
My bet's that the ocasionally harsh treble lies in the HB 1's tweeter. As much as I like the Heybrooks -those boxes are great fun!- their dome tweeter's a bit unrefined. Has always been so.
What cables are you using? DNM Reson by any chance? I'd try some cheap and cheerful OFC cable, like Van Damme Blue Studio or plain thick 322 stand one, before bying a new amp. The Cyrus is a peach.
Of course the above-mentioned Creek CAS 4040 will cost you less than a pair of terminated cables. It's indeed a bargain and would sing wonderfully with the HB 1's, even though I doubt you'd come off with that slighly abbrasive treble.