32 ohm means it can be driven easily, i.e. just plug and play to the source, like iPod.
250 ohm sounds best if it's driven by a dedicated headamp.

But as a full-sized headphone, not many people will bring DT990 out.
I suggest u go for 250 ohm and try get a good headamp.
You should try to listen to 600 ohm, lagi shiok!... hehehe!

I'm using DT880, 250 ohm, bought 2nd hand as no money to get the brand new 600 ohm.

crossroad edge is good amp imo but its lack in driving those 600 ohm cans
gave distortion at 1 o clock volume when pair with my dt 880 600 ohms but they rock with 250 ohm dt880
IMO it is well built and look small for desktop amp not to mention cheap and affordable ( it is a ss amp btw)
well u can try with beyer a1 which is i think way out of budget but it heavenly match with any beyer cans ( a class A amp )
have u try the heed canamp as well? Drive my dt880 like a breeze and my hd650 as well
i think it is affordable for price and 1 of the best amps outthere (class A amp as well) 

i think the 2005 version (250ohm)
sukhoi i think i saw u at jaben last week
was it u trying out the hd 650 with traformic tube amp? and the darkvoice 337se?

yup just tried the tralafomic tube amp 
ohh that uncle favorite cd player (original)with inbuilt dac 
i go there once a week jus to check new amps and stuffs
tried the corda as well great poison
wanted to try gilmore lite but uncle forget where he put afterall
dv 337 is great issit? pair with any sen and u in audio heaven aledi
Maybe i will c u there next week 

lol 
there is onli 1 uncle who say young man can i help u and join the forum when u leave the shop 
too bad the darkvoice332 is under repair but 337 is a great deal jus a bit of scratch but it work great otherwise
try the gilmore lite i sure u will love it bigger soundstage and sound signature is more like pico warm and very sweet 

well if u come to sg i will be 1st to introduce u to uncle wilson but wait i think u been there lol  yur pic of jaben and beyers cans
his store jus moved to better place (jus 3 door down but same floor) bigger and more space 
all kinds of cans there for sale u name it u will get it there uncle just got his stax and akg 1000 not to mention baby orpheus still hiding somewhere in there
afterall i know u too well hahahaa 

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Added on September 8, 2008, 2:10 ambtw guys is any gathering in nearby future?
wanted to c some new cans and audition them as well
of cos i will bring my dt880 600ohm for audition 

well i stay at tiong bahru but coming back to msia this sat
got wedding dinner to attend
if got gathering nearby future i dun mind coming down to msia to auction actually
i will bring my rsa predator (if any of u r interested in trying ) and my favourite cans as well
btw jaben also got dt880 600 ohm for auction as well jus ask uncle bout it and he gladly hook u up
but BEWARE u dont to be deeply poisoned by it (how i got hook and next day went to get it)