Finally got my Shure SRH1540 and I am writing this as I am listening to them...
First impression? Expectations exceeded and very impressed!
So far I have played many of my higher res music (24/96 FLAC tracks) through it ranging from Bill Evans to DEATH and TOOL and it all sounds excellent, even when just using a Focusrite Solo (3rd Gen) with its balanced output as the interface with my PC.
Looking forward to getting to know these headphones and happy to say I feel no need to invest in a second pair of anything for the time being