Oh Smeggy you lucky boy .
I am interested to know, how are the capabilities of the T30 driver in reproducing large deep bass in comparison to the NADRP18? (I am under the assumption the NAD and its brothers are probably the best ortho in this respect).
And wow that T30 mod looks beautiful. I never liked the original housing that much. Gotta say though, not a huge fan of that headband .
They look in lovely condition!
Its all about tuning the damping on them. You will lose some bass quantity, but should increase the 'impact' of the bass as it gets tighter. Iv not actually tried tuning the YH-1 yet, but if you want to retain bass, maybe my progressive donut damping method might* work...
Also, on hf, Billink has made his own damping scheme on the YH-1, that makes him love them for classical music (and he owns an O2!).