I like your amp, would not consider it mid-fi, a very nice mid-powered tube amp, which I suspect sounds very nice. A bit more power than my Cayin A88T using KT88s 45wpc.
now, your BEAUTIFUL speakers, sensitivity 86 db is NOT easy to drive from a watts/sensitivity perspective, I think the designer is meaning, it's mostly constant 6 ohm impedance curve is not hard to drive.
Probably so, but I would want more power reserves for any speaker with low 86 db sensitivity, for instantaneous peaks, or bi-amp them.
IOW, unlike some KEFs, etc which are difficult to drive, with very low dips of impedance, yours's are consistently near 6 ohm, easy only by comparison to difficult speakers to drive..
So, I would consider the speaker, not the amp.
1st, I would try stuffing up the port.
It is a transmission design, seems a nasty thing to go against it's method of achievement, however, perhaps it's bass ability is masking it's mids.
a. partially with soft diffuse material, across the face of the port
b. fully with some dense foam
Perhaps with some bass cut, the mids will be very nice.
2. move on to other speakers, higher sensitivity, and one not trying for too much bass which I think can be a mistake people make when reading numbers.