From the sound signature i get with my DT 550 and the 0404USB, i'll bet the MS2's will sound very punchy and crispy, the stereotype solid state sound if you'd ask me.
And if on some later moment you decide that the sound is not what you are looking for you can always couple it with a more tubey amp.
E-MU 0404 USB + MS2i = yes, nice, and as noted above, it can also serve as just a source so you can add an amplifier of your flavor later on.
Just don't use the PCI E-MU since it has no integrated headphone amp.
I have the MS-1 together with a Millett Hybrid amp, and it sound great.
I'm also planning to get the 0404 USB just as a source. I don't think I'll use it as a amp, because I found out that I like the slightly warm sound I get from the Millett's tubes to my previously used SS amp.
If you're looking to get warmer sound I think you'll reach the same conclusions as me - Alessandro's are already very punchy, and tubes just make them great.