Too many choices, NEED feedback on tube amp.

Have you thought about the WA6SE? The extra power they provide for low impedance headphones is not negligible. It's far better at future proofing yourself than the WA6. I had the WA6 and returned it for the WA6SE. The SE is just so much better.

Not sure if anyone can make recommendation without knowing your music preference etc.

Also, is tube rolling, resale value and such a consideration to you?

Haven't listened to any one of those amps, but a 600 ohm Beyer should be compatible with pretty much any amp out there.

If you want to go with tubes, I imagine you want the tube coloration? If that's the case, go with a transformer-coupled SET: it adds a bit of sweetness to the vocals. They also have the advantage of better bass control and greater compatibility than OTLs, but transformers are not cheap.

Since you are in Canada, go local and buy the MAD. Though it is $700.

Oh, and by the way, realize that you are basically asking for a comparaison between five different amps. Few have heard one, let alone two or more, of the amps you have listed. People come to look at your thread, realize they do not have the knowledge to help you in your choice, and leave. That "ridiculous" coment was uncalled for.

Those viewers probably had the intention to help but couldn't.

As you probably expected, people buy one amp that gets the job done and that's it for them. They don't usually bother doing comparisons. Owning 2 $600+ amps is ALOT of money.

I've never used a high impedance headphone on the WA6, but I didn't find it powerful enough for my low impedance headphones. You should still go transformer coupled if you plan to use low impedance headphones too, but the WA6 wasn't good enough to justify $600. The sound was not much different from my Ibasso D10. It was simply warmer sounding. The 6SE is a completely different story, but now we're talking almost twice the price. I would probably suggest a better solid state amp for low impedance over the WA6, though I am sure it would be great for high impedance headphones. But... I would rather save the money and just get one amp to do it all.

there is always issue of folks having no respect to others, but I don't think that is the case for this thread.

You did your research and came up with the list. Grabbing the first affordable one should be the next step. 

For sale forum is your good friend and there are other options. Also, not that I recommend taking advantage of it, but I believe most if not all of the brands you listed has reasonable return polity.

Or maybe changing the question to 'which amp is the best match for DT990s' might work :)

Get the Woo 6.  I own a Woo WA22 but I got to listen to the 6 through my old phones which were AKG K701's and my new one's the beyer Tesla T-1.  I was a believer in about a minutes time.  It was that good.   Skip the Sophia tube upgrade if you are thinking about it at purchase time and buy the EML from here :http://www.tubeaudiostore.com/eml5u4gmesh.html or TubesUSA but he has a higher ship price.  Or buy from Jack Wu.  I saw your budget so you can just enjoy the amp, save up and buy later.  The amp sounds great and looks beautiful plus it it hand built in the US.  There is a separate thread for Woo guys at http://www.head-fi.org/forum/thread/428570/woo-audio-amp-owner-unite  Everyone over there is very helpful.  

If you are really on a tight budget and don't mind waiting you can keep an eye on Amps For Sale because these do pop up.  You could probably get one with upgrade tubes for the price new w/o tubes.