what type of music for Grado SR325is?

rock, house,trance.

Rodrigo y Gabriela on infinite repeat. That album was made for selling Grados. If you listen to that album on a good Grado and don't end up buying a Grado then something is wrong with you.

I'm going to break with the groupthink and mention some non-rock music styles that I like on my SR325is.

Jazz: like Sonny Rollins; Medeski, Martin & Wood; Chick Corea; Jaco Pastorius; etc.
Blues: traditional, electric and acoustic; Stevie Ray Vaughan, Roy Buchanan, Keb Mo
Bluegrass and bluegrass flavored music: like Jerry Douglas, Russ Barenberg, Edgar Meyer in "Skip, Hop & Wobble"; Bela Fleck in "Drive"; etc.
String quartets: yeah really, string quartets become interestingly involving

That's not meant to be an all-inclusive list. Apologies for all of the fine Grado music I left out.

Amp preferred,not a necessity.
There will be adequate bass.

I haven't tried my SR325is unamped or with any amp other than my AV123 x-head.

I would suspect that an amp that sounds fine with the Denon D2000 will drive the Grado fine and sound fine with the Grado. Just make sure the amp isn't overly harsh in the high end cause the Grado could accentuate that. The SR325is has more highs than the D2000. So if the D2000 highs sound harsh to you with a particular amp then the SR325is highs will probably be moreso. I don't have any complaint with the SR325is highs with my setup with my ears and my music.

Bass on the Grados is mix of auditory illusion. The Grado bass rolls off a bit early for my tastes. But the Grado compensates with a bit of a bass hump before it starts the rolloff. That bass hump gives the bass some punch and makes it sound like there is more bass than is really there (that's the auditory illusion part). The hump usually manages to catch the bass drum so the bass drum in rock music still gives a necessary punch and drive. The bass is tight and controlled. Compared to the D2000 though it is missing the low stuff.

Some music will sound bass-lite. With some rock I have been left with the feeling "whah? where's the bass". For example Iron Maiden "Piece Of Mind" the bass is a little too light for me. I compensate in those cases with a bit of DSP virtual subwoofer (sacrilege, I know). So watch out for bass-lite rock. Keep in mind though that I'm well adjusted to the D2000 level of bass and I really like the D2000 level of bass. I also haven't done any of the basshead type mods on my SR325is, things like trying flats, tape around the bowl pads, reversed bowls, or anything like that. I'm still using the stock bowls.

Jazz. Especially well recorded live jazz.

Amp is optional, there has been a debate on Grados benefiting from amps.

 

As for music, I really like edgy music.  All types of metal, classic rock sound great on it.