Subjective sound description:

The HD58X has the best bass extension of Sennheiser’s HD6** series headphones. Bass is present and ‘tighter’ than that of the HD650/HD6XX. No loud deep exaggerated ‘rumbles’ in this headphone even though bass extends down to 20Hz (-3dB). It won’t rattle your teeth nor appeal to bass-heads.
Integration from bass into the mids is excellent. No ‘dis-attached’ or ‘fatty’ bass at all. Bass-lines are easily followed and sound very natural. Bass extension is MUCH improved compared to the pre-production model I reviewed earlier.

The mids have a somewhat ‘warm’ character yet still have good clarity/presence. The overall sound signature is in between the HD660S and HD650 when it concerns the mids. The HD650/HD6XX sounds somewhat ‘softer’ (as in ‘romantic’). The HD58X, just like the HD660S sounds a bit ‘fresher’. The mids are dynamic and appear audibly ‘free of distortion’ as in clean and ‘natural’. The stereo image (width) is about equally ‘narrow’ as that of the HD650 and not an aspect the HD6** line-up is famous for.

To me the HD600 is the ‘brightest’ and ‘leanest’ sounding ones of the HD6** headphone line, but also slightly more ‘boring’ than the HD58X, HD660S, HD650 and HD6XX.
The HD600 and HD650, on the other hand, are slightly ‘smoother/softer’ (in texture, not level) in the upper mids/treble and a bit more ‘forward’.
The HD58X (and HD660S) are a bit more ‘dynamic’ and ‘lively’, a bit ‘fresher’ sounding.
The differences between HD58X and HD650/HD6XX are not very big though so don’t expect a totally different headphone or a much darker or bassier HD650. These are quite close.

Mids and treble are seamlessly integrated. The treble is on a ‘neutral’ level. Not recessed and not emphasised. The pre-production model had elevated and sharper treble. The current HD58X is closer to the HD660S and HD650 in treble level.
The HD58X does have good treble though. It is ‘fresher’ sounding without becoming splashy or sibilant. When you are sensitive to sibilance (like me) the HD58X is a good option.

Whether one prefers the (still sold new) HD600, HD650 (HD6XX) or the HD58X/HD660S remains a personal thing.

A short sound description would be:
A somewhat ‘warmish’ headphone with good ‘presence’ and treble quality and quantity.

One might think the HD58X Jubilee is a poor man’s HD660S and would not be far off in that assumption.
The HD660S is somewhat more ‘refined’ and ‘tighter/neutral’.
At this price-point the HD58X is very hard to beat.
The good news is that with some small modifications the HD58X can sound VERY close to the HD660S for just a fraction of the HD660S’s price.