is there any way you can program it that only sounds your own mech are producing are being processed by the client. It might not give the full immersion but I don't believe one mech will fill all 64 sound channels 
I also believe 64 isn't an arbitrary number, some kind of unsingned int ? maybe turn that into a long 
although that migh be oversimplified to think then to do
No, 64 is not in fact a completely arbitrary number, even when you disregard the base-2 nature of modern digital computing. There are a LOT of all different kinds of sounds going on all over the place, and KingLeer and the other devs have done an astounding job just getting it to sound as good as it does.
Problematically, however, they are attempting to push Crysis to - and in some cases beyond - its original spec in order to accomplish all they feel it can and needs to do in order to make this the best and most realistic Mechwarrior game ever. In doing so, they're running up against aspects of Crysis that have never been fully tested or flexed, or where Crysis' capabilities still perhaps exceed those of most peoples' hardware and/or drivers and operating system. There's a lot of cross communication going on all over the place, and sound detail has long been notoriously tricky to do right sometimes, and CryEngine in this case is no exception.
Between footfalls, torso twist noises, weapons fire, environmental effects, etc., with just you alone in the server... well, I dunno for sure, it'd have to be for Leer to say, but I'd guess you might use between 8 and 12 channels, maybe as many as 16 in extreme cases. Now add other players to the server, whose own actions have to be synced across the network (for many reasons, including sound effects) and the processing that has to be done to determine which of the noises made by other players should be replayed locally, at what volume and on which channels, and it can start to get pretty complex pretty quickly, filling up 64 channels with relative ease. Keep in mind it's not just your sound card being used/affected in this equation, your CPU(s) and system RAM are heavily involved also.
Unless I'm *completely* off my mark, anyway. Leer?
