100% THX00 are nice headphones stock. Unable to return to stock may be regrettable if you dont like mod or want to resell later.Before anyone decides to go open, please consider only reversible mods.
TH500RP cups do make the bass go halfway to dirty HD6XX bass. Its the smooth & warm tone ala 6XX that makes it worth consideration. I find stock ebony a niche headphone in my collection: good closed can. TH500RP cups brings it more to a good all-rounder. Going to need some light damping like @SHAMuuu said to get it to great level.