Thanks for the replies, all very helpful! I'll introduce myself a little better tomorrow morning, it's been a long weekend.

I looked at the previous posts regarding the THS4032 and people describe it as 'dynamic' and 'forward', which I'm not sure if that's what I'm looking for. Just to give you an example, on Johnny Cash - Help Me before I would really feel the resonance of his guitar, the pluck of the strings etc. while it's still there (and more) it feels a little buried or something. I can only describe it as a veil for the lack of a better word. Maybe it could be the presence of proper bass is bringing something else to the table, this may account for the flattened sound.
The only reason I mention this is because when I first got the K701s, guitars really grabbed me. I know it can sound that good, I just want it all!

I mostly listen to rock, or 'anything with guitars in' so I would definitely say it is a sound that I actively seek out.

Though despite what I've just said, I have been flicking through tracks and the percussion / rhythm with the 4652s is absolutely fantastic. Drums crash rather than splash, plus all the other goodness that comes with it. Truly stuff to gird your loins with

Stan mentioned the MCL5/6 mod to me specifically when I picked up the unit, if someone else can confirm what Gazjam is saying, it's very likely that it'll be the sound I'm looking for
Looking at Leo's post above, the capacitors are in the analogue part of the circuit, so it would make sense that removing a bit of filtering could open up the treble. Fingers crossed!