Wow, these things sound amazing. Better than any other full size headphone I've owned. I used to have the HD428 (closed) but they were vacuumed up and the cable was ripped out, which is why I upgraded to these. I think the DT990 PRO 250 Ohm is very much worth the $200. The HD650 is around twice the price from what I see; haven't heard it but for that price range there are other headphones to choose from that may benefit a specific genre or wide variety of music (the HiFiMAN HE-400 is another good headphone I've heard about in that range). In general, as you might have guessed, these provided a greater sound stage, more detail, and less isolation over the HD25's. The DT990's give more of a concert hall sound, compared to the studio room sound of the HD25's. The imaging is definitely better on the DT990's. These are out-of-the-box impressions btw. Burn-in might help; still not sure if I believe in that or not. Anyway, I tend to keep the E17 EQ at -2 for treble and 0 for bass for most things. I think the sig pairs well with the HD25's; but there are some differences. I won't go into detail because I haven't heard the DT1350's. My music is FLAC from my PC and iPhone 4S. I listen to metal, punk, electronic, jazz and classical. The volume of my music varies, due to the nature of the music and recording/mixing. With 0 gain on the E17, I have the volume set from anywhere from 45 to 60 but increasing the gain helps a little bit as well. Might be different for you as I like some music loud. I also have a FiiO E09K for desktop use which more than enough to amp these with the E17 docked for use as a DAC. I also watch blu-rays and play games on my PS3. The DT990's give a theater-like sound and make everything more immersive. Whether the games were FPS or RPG, I was very satisfied. Voice acting and other sound effects also improved. It might be worth mentioning the PS3 limits Linear PCM blu-ray audio to 16/48 through optical for some reason but still sounds very good. I would hold off on upgrading to a different AMP/DAC and stick with the E17 for now, unless you feel like you need more volume for your recordings. The E09K is nice but, for the DT990's, I don't think the extra $100 spent is necessarily needed. Comfort wise, the DT990's are amazing. The clamping force of the HD25's makes my ears sore and gives me headaches after long periods of use. The DT990 PRO's clamping force is strong enough I don't have to worry about them falling off at all. The large, soft pads provide extreme comfort. Every year, I participate in a 24-hour gaming marathon to raise money for hospitals. I can say with these, the event will go a lot smoother without bothering anyone during late-night hours. I find the DT990's to be pretty durable but I bought a travel case for storage since the packaging for the PRO version doesn't include one; I don't feel like I should throw them around like I do with the HD25's. I think the DT990's handled whatever I threw at it pretty well; a very good overall headphone for the price. Hopefully, my newbish comparison will help you in some way.