That's a much better test then! Did you apply appropriate dithering and noise shaping in your downsampling process? And what tools were used?
You would of course notice a "difference" since the HD800 and HD650 are not voiced very similarly at all. More stark than any quality difference is simply the signature difference.
However, HD800 is famous for being remarkably picky and revealing of the rest of the chain. E9 is "more than minimally adequate" for HD650, however the HD650 can do much better than that, so if you're going to be upgrading to something like HD800, it may pay to get more out of your HD650 first. Beyond that, HD800 has something of a notoriety for harshness on gear it doesn't like, and some people who have upgraded to HD800 find they actually found it less enjoyable than HD650 and switched back. I love the HD650, it's still among my all-time favorites, and what it does it does very well, though from a technical standpoint, if EQ'd to taste (a.k.a. get rid of the horrid treble shelf) it is definitely more capable. But the result of HD650's tendency to make even harsh sources/recordings sound pleasant is a strength if you're not pairing it with the best of gear. HD650 can do better than E9, but it can certainly sound good on E9. While I no longer have E9 to test, I highly suspect HD800 may not sound quite as pleasant on it. It sounds like you're using a PC as a source though, and with appropriate EQ, it's still possible you may like it more... That's a tough call since while E9 isn't really up to HD800 caliber, it's not an entirely terrible amp, either... If you get a chance to audition the HD800 with your E9 somewhere, that may be more helpful in deciding what route to go!
i am read a review of e9 where it is used with higher end headphones on low gain settings... it was found to have adequate power levels but not that good quality wise... although according to the review, hd650 went quite well with the e9... i also think that i should improve on my amp/dac combo first, which more emphasis on higher quality amp first....