As an owner of Altecs you probably know that exquisite midrange is not a trait exclusive to Harbeth. Many speakers in that price range are equals or better than the C7s in that regard, so no good reason to limit your amp choice to those unless you’re absolutely smitten by them. I would personally want a speaker that has far greater dynamic range, i.e. one that can wake up at low volumes but also play loud without obvious compression. The C7s can do neither IME.
Definitely consider the Spatials if your space allows. The Seas A26 is good if you don’t mind a little DIY.