Unless you have an expensive set of cans, you don't really don't need the XDA-2. It's a DAC and headphone amplifier. So you are paying for the headphone amp. The benefits of the balanced outputs will probably not make it worth the cost. You'd be better off to spend the money on speakers.
For that matter, many people on here might say that the ODAC and the Schiit Modi that I recommended in your other thread would be overkill (btw: stop starting new threads--it makes it hard for people to respond with all these different conversations). The ODAC has been tested extensively, and is show to be audibly transparent for reproducing the source. No need to go better than that. I've seen people compare the Modi to the ODAC who found them equivalent, which is why I recommended it as a cheaper, although less portable option.
Save your money for buying more music
Your questions are answered:Speaker FAQ Living room HT: Energy RC-50, Ascend Sierra Horizon w/RAAL, Ascend Sierra 1, PSB Imagine XA | PSA V1500 and CHT SS 18.1 | Denon X4200W | modified Dayton SA1000 Other rooms: CBM-170 SE | SVS SB-1000 | Audio-GD NFB-11 | Parasound Zamp | JBL LSR305 Headphone & Portable AKG K7XX | NAD HP50 | AKG K550 | Soundmagic E50 & E80 | DX50 | E12 | X1