Hi Trenton,
Welcome to the forum, and thanks for your service to our country.
As far as the DACs go, I actually have the HRT MS II+, not te basic model and I have had the bifrost in on demo, but have never heard the Little Dot or iDac. The basic (non + version) HRT is pretty good, especially for the money, but in the long run I think the bifrost is a better long term choice. It is somewhat better than even the HRT MS II+ (in stock form) but if more flexible, plus it has the ability to upgrade in the future, which should make it a better long term investment. Of course the HRTs are limited to 24/96 and the Bifrost can do up to 24/192 -- again, even if you don't have any 24/192 files or sources now, you probably will at some point. The caveat here is that the usb input on the Bifrost won't support the 24/176.4 rate at this time -- a bug in the code in the usb receiver firmware that CEntrance is working on a fix for. This does not apply to the toslink and spdif coax inputs -- they support all sampling rates.
Perhaps I missed it, but what will your source be? If a computer, you can always add a usb -> spdif converter later on (the Mapleshade Reclocker (a tweaked version of the original hiface, and far better than the hiface) and a bargain at $184, or yyou could wait until the firmware gets fixed (if you need 24/176.4 capability now) and then potentially use the coax and toslink inputs for other sources later on. Or, you could buy the basic bifrost without the usb board and then get the Mapleshade reclocker spend another $84 over the price of the usb-equipped dac and have a really very nice setup that again, should keep you in the tits for a good long time to come. You also don't need a usb cable with the reclocker as it plugs directly into the computer or laptop.
However, if you do plan to go usb, I definitely recommend an upgraded cable -- you don't have to go wild here -- the WireWorld UltraViolet and Starlight (basic, not the silver of platinum) are wonderful cables for a very reasonable price and a definite step up in sound quality. Another excellent choice is the AudioQuest Carbon -- though the two models below it don't do much for me.
Or, if you have a 2011 mac mini, you can do direct via a decent glass optical cable to the bifrost and get really nicee results too.
And just to confuse you with one morescenario, if you used usb from a computer or laptop, and used the coax fed from a cd player or transport, you could get something like the Cambrridge ID-100 and plug an iDevice in via the optical -- then you can have up to three sources you can select between with the front panel switch.
Of course, if you want another, completely simple alternative (assuming you are using a computer or laptop) that involves no need for special usb cables or interconnects, is limited to 24/96 and provides surprisingly nice sound for the money, the Halide Design DAC HD is a real winner, and IMO sounds better than the bifrost.
I returned my bifrost and kept the Halide for my headphone system
Sorry for the information blitz but of the dacs listed above and the Halide, I don't think you can go wrong -- my fave of th lot is the halide and by a pretty good margin.
Hope this helps more than confuses :-),
Jim