I've been very happy with my HRT Music Streamer II+ for a long time. Far from laid back, it was a huge step up from my old Music Streamer II. Makes the old MSII sound super tame. I've also heard the Modi and ODAC and neither made me sway my opinion for better or worse. I also find it to be a fantastic match with my BH Crack.
Dude! You just got the HD 650 and you want to upgrade!? Listen to what most people are telling you and ENJOY your current set up. The HD 650 is a flippin' great headphone! Seriously...sit down right now and listen to some music with them. That's not advice, that's a prescription. If down the road you really want to try something different and/or want to work towards an "end-game" setup, then get the HD 800 and be done.
I understand the excitement over the HE-560, but I REALLY want to hear more about the HE-400i. If it's a clear upgrade to the HE-400 I'll be there day one. The HE-400 is pretty much my go-to can for electronic music, so if they tweak the treble a tad and keep improving the already superb bass I will be one happy man.
The reduced weight would just be the cherry on top!
Many would disagree ;) But really, cables are the very last thing I'd upgrade, you really have a great setup now so enjoy it! If you really need to keep spending money, get a bunch of tubes and tube roll. Other than upgrading headphones, you'll be getting into diminishing returns territory for your cash.