analog is random and it differs from device to device.
you'll get lots of difference in sound

digital makes use of a soundcard (or we call it dac) inside the speaker so no matter what you connect it'll sound the same.

up to you on how you perceive sound so... some people wants a constant sound, some wants better via analog, some just wanna experience a rainbow of sound

plus if you're a sound engineer traveling with your studio speakers, you wouldn't want a different sound signature. You want a constant sound for your reference in work. (it's like how musicians prefer to use their own instruments rather than using something they are not familiar) (but then again I believe no sound engineer uses digital connections)

hope it helps explain why the difference in connections.

I guess I should say some words since I've tested both Studio 8 and S530D in my room

It's either you get the Studio 8 or opt for Edifier S530D (you can ignore your other options)

S530D will give a harder kicking bass compared to Studio 8 mellow bass

Both pounds hard
Both gives clarity

In any case you need rock, these 2 are just not meant for it due to its massive sizes contributing to sluggy speed while rock needs things fast. (however your 2nd option R2730DB can do it)

but hey, they're both superb speakers to invest in so I'd definitely recommend choosing either one.

I'd go for Studio 8 if you got the table space mainly because it sounded more 'huge' compared to S530D (plus the amp could save you some electric bills)

I own the S530D and technology wise it's outdated. But sound wise I'll always go back to the S530D when compared to Studio 8 because it has more warmth over Studio 8 cold feel

Hope it helps in your decision
If you can't decide... Just buy based on looks
That's what I do most of the time nowadays. Cosmetics>Sound
I should be punished someday