P Atkinson SOTA - what's going wrong


I'm new here, but have been getting excited about music and hifi since childhood.

Last year I inherited some DIY built, P. Atkinson designed 'State Of The Art Loudspeakers', as featured in the HiFi News and Record Review April 1976.

I listen chiefly to digital files (FLAC), through a Pecan Pi DAC and Temple Audio Monoblocks. This system works beautifully on my smaller room speakers (Linn Index), and also powers the SOTAs very nicely, although I can't get away from the fact that they're very fatiguing to listen to. I'm very fond of them, visually, and for the low frequencies, and for the back story of having been designed and built by enthusiasts sharing designs in magazines.

So I'd like to make them work well for me.

The drivers are

KEF B139
KEF B110
Celestion HF 1300 (8 ohm pair)
Coles 4000

I suspect that by now the crossovers will need re-capping, and that this may be the main issue.

I'm also considering replacing the B110s with something newer. What's confusing me is that when I removed a B110 to explore the cabinet fitting (in view of replacement), then listened without it - the fatiguing aspect disappeared. There was certainly a 'hole' in the midrange, but I'm astonished by how much detail is coming through the HF1300s and the B139. More than I can usually hear, because I suppose the B110 is spilling over everything. When I switched the other monoblock on to listen to the same passages through the intact speaker on the other channel it seemed almost unlistenably bright in comparison.

So, could this be the B110s themselves, perished after 40+ years, or should I suspect the crossovers are dying and leaking frequencies all over the place? I feel like I've had a little insight into how could these could sound if I just get that midrange back where it should be.

Apologies if my terminology, or very basic tech knowledge is way off, I'm quite the novice, but I'd love to understand more about getting this system singing.

Thanks in advance