Sorry, just my honest opinion.
I feel that I can give this opinion with some authority being an amateur guitarist/bassist.
I don't dislike the HD540, but both my SHP8900 and HE-500 has better bass extension and both are to my ears a more well-rounded sonic experience.
Never apologise for having an opinion that differs from someone else's. Your opinion is just as valid and gives other readers of this thread an alternative viewpoint.
Guitars? Tell me about them!
I'm a fan of Hifiman can's, I've owned the (comparatively) bass rich HE-400, and I've owned two pairs of HE 500's, the last pair I sold a couple of weeks ago.
I compared the HE 500 to a pair of Senn' HD 700's, the 700's beat the 500's hands down for sound stage, on certain tracks I would have to listen carefully to hear some background instruments with the 500's, the same instruments would be more noticeable on the 700's.
This in part could be down to the bright signature of the 700's, far too bright and harsh on anything less than well engineered tracks. The treble on the 500's much smoother and forgiving on poorer recordings.
Lovely bass on the 500's, and the bass on the 700's I found to be pretty close, but the 500's get the nod because of their more refined treble.
For me the 540's are a more 'linear' headphone than the HE-500, no they don't quite have the same bass impact but the treble and midrange are more transparent.
My findings are based on having Beresford ancillary equipment, other readers might come to a totally different conclusion than me.
If I was forced to own only one pair of cans and those cans had to be HE-500's then I would be very happy, but on balance I'd rather be forced into owning a pair of HD 540's.
Bang for buck? HD 540's can be purchased for around the £100 mark, second hand HE-500's sell at £350 all day, are HE-500's worth 3.5 times the cost of the HD 540's?
In my opinion....NO. The law of diminishing returns really kicks in on this one, HE-500's are excellent cans that beat the HD 540's on bass performance and bass performance alone.
At £100 or so the 540's really are a 'no brainer'.
Now if someone can point me in the direction of a pair of cans that produce the sweet linear treble and midrange performance of the 540's, combined with the bass or even more bass than the 500's, at a sub £500 pound price point (even second hand) I'd be VERY interested.