I really don't think you're going to get a better experience with your new Titanium HD over your ZxR, however I know that the open backed AKG's require a damned good amp to drive them to their fullest so your question is relevant. An external amp may well help with these headphones, then again you could just keep the ZxR and try using an amp on them..... whether this helps in just games (as opposed to music) using AKG's, I don't know. Do a search and see how people get on with AKG's with ZxR's. There are a few AKG readers in this thread, so hopefully they can help.
I've played Arma 3 - it has a better soundscape than A2, but they've got a lot of work to do on it - just adding reverb is a bit of a con for the time being - though it's a lot better than Arma 2's in theory. BF4 have yet to buy.
Personally, I went with the new SBZ range..... just better everything over the older X-Fi's, unless you're looking for legacy games support.