1 - All my games are digital now.
2 - Enough with the digs on the Xbox One. I still like it significantly better than the PS4 and I can't tell the difference between 1080p and 900p or 30fps and 60fps. I really don't give a flying **** about the power difference between the systems. There's only one game that I want on the PS4 that I can't get on another system and even that is just a remastered version of a PS3 game. The UI sucks, the PSN is unreliable, I get kicked out of party chat randomly, etc. The PS4 is a ****ty purchase right now, even at he price I paid. Literally the ONLY reason I got one is to play with friends who stupidly got one instead of an Xbone because it's more efficient for me to buy one console than for all my friends to buy a second (many of whom couldn't even if they wanted to). Shall I go on or shall we all agree to drop the subject like mature adults?
Re: your first question, if there was an issue with the double-amping, it would have been mentioned in the guide.
Re: your other questions, if you want something that works on console/set top boxes AND PC, the only option is the Sound Blaster Recon3D, which uses THX instead of Dolby Headphone. The Recon will do audio over USB if you have it in PC mode (like an external sound card basically) and over SPDIF if you have it in PS/Xbox mode.
The problem with the ModMic IMO is that you still have to deal with a second cord. If you're going to do that, I'd just as soon get the cheap clip-on mics that are $5 for 3 of em. I have no issues with the SQ on those cheap mics, so the only reason I'd upgrade is for something like a Boompro, which fixes my cable clutter.