YMMV but I have owned 275’s and SHL5’s but at different times. I presently own O96’s.
I was initially drawn to the 275’s because of the texture it imparted and over time that texture subjectively became mildly grainy to me. The SHL5’s are nice (Ive never experienced the plus version). I don’t know if the running out gas impression is the Mac or the Harbeth but I would consider a very nice a or a/b solid solid state amp if its the Harbeth’s you are trying to match to. The upper end on the SHL5 is not their best effort (when compared to, say their 30.2’s). What is it you are trying to build from? The amp or the speakers?
I was initially drawn to the 275’s because of the texture it imparted and over time that texture subjectively became mildly grainy to me. The SHL5’s are nice (Ive never experienced the plus version). I don’t know if the running out gas impression is the Mac or the Harbeth but I would consider a very nice a or a/b solid solid state amp if its the Harbeth’s you are trying to match to. The upper end on the SHL5 is not their best effort (when compared to, say their 30.2’s). What is it you are trying to build from? The amp or the speakers?