What DAC are you using? buying a Master 9 or high end dac will better your decent Asgard amp compared to buying a high end amp with mediocre dac. I'm still quite shocked how many here put emphasis on a amp more than a dac. How you approach spending on your system is upto you of course I"d go source than down the chain. You've already purchased the Hd800s so your already stuck with that specific sound signature. The 400i you has less detail but it's more of a chillout non critical listening headphone that is very decent for the price. The HD800S is crystal clear and also lacks bass but people buying such headphones should know that already. For my ears and preference the bass from the HD800(s) is just enough as I'm not a bass head. If you buy a high end amp that is great as it's part of the equation in great SQ. However like anything if you have a system with weakness you'll definitely hear the deficiency. A better dac with "good" amp will sound better !!!! Cheap dacs just sound average regardless if you use the best amp in the world. I say the Headphones/speakers > DAC > AMP in how much impact the sound quality will change. Having all 3 as you max your budget will reap the best sounding (personal preference). I still think the Hd800 (s) is an overly stimulating headphone for true chillout relaxation . However when you want the "detail" fix it'll deliver. I urge you to test the He560. It's a noticeable step above the 400i in overall SQ. I'd rather have a decent amp and excellent DAC and use the leftover cash for a different set of headphones for a dramatic sound quality difference.