Hey all, audiophile noob here. I recently got myself the Sennheiser HD 598 which is running through a Asus ROG Phoebus sound card. My game was changed going to open-back and a well known name, so yesterday I went ahead and also ordered the HiFiMan HE400i and AKG 712 Pro. I signed up for the Massdrop Creative Sound Blaster X7 and am really hoping it goes through, but if it doesn't, I am not going to wait around. I have been eyeing into a Schiit stack, but am also wondering if these 3 HP's that I now have would be best with a solid-state or tube amp. Also, two major features I liked about the X7 is two headphone inputs and an digital optical in and out (could finally use my 5.1 system with my computer, my sound card with windows 10 doesn't allow digital to analog optical 5.1 for some reason). Thanks for any info, I've been researching this past week a lot but I'm not seasoned.