I'm going to tell you how things are now. Over the next few months as linear 4K becomes available, things might (surely will) change.
Assuming you don't already have an HR34, then a regular Genie upgrade would be an HR44. You might get an HR54, but you don't have control over that. For 4K, you need the HR54 AND either the C61K client OR a DirecTV 4K compatible TV. The HR54 can't do 4K on its own, it does not have the necessary decoders etc. Unless you buy all the stuff yourself, you won't be able to get the 4K equipment until you have a 4K TV, because DirecTV installation is mandatory and they won't install unless you have a 4K TV.
The C61K can I believe do 7.1 surround if this is available with the programming. I don't know if DirecTV (or its program providers)will deliver 7.1 with linear 4K, we will have to see. I suspect the Hr54 itself won't do 7.1.
A lot of this is "informed speculation". Although the recently-mentioned test of linear 4K will use an existing satellite/transponder, production linear 4K is expected to use one of the reverse band transponders so you would also need a new LNB at the dish.
Don't bother to ask DirecTV about this. You'll get no info, incorrect info or confusing info. Just keep watching what Scott posts on this forum (see
http://www.satelliteguys.us/xen/threads/live-4k-broadcast-on-directv-this-month.357306/#post-3821928), and the info at the edgecutter forum that Scott has mentioned in his posts. Several people on the edgecutter forum have all the equipment we think is necessary for linear 4K but we'll find out soon.