I've just re-set my own Devon energy and roll off controls as you've suggested and I now have speakers I can enjoy! Cheers for posting your advice. I'd always assumed the controls should have both been set at the neutral positions. No wonder I couldn't live with the treble response. Only taken me several years to suss this! Better late than never I suppose.
I was going to go down the valve amp route (hoping that would tame the treble) but no need now. However, my trusty old NAD 3130 is a bit past its sell by date so wondering what might constitute a good replacement.
Thanks again Paul (Reffc) for posting your advice here.
Mike