That Xonar U3 looks like amazing value for money, and a great option for laptop gamers (finally!) too. I might pick one up for a friend who games on a laptop.
Re: Dolby Headphone on U3 vs DH on PLYR1, I'd just assume that it's the exact same tech so the execution is equal. In fact, if I was gaming on a laptop, or strictly at my desktop, the U3 looks like a good alternative to the PLYR1 entirely...why pay twice for the same feature (Dolby Headphone)? The PLYR1 makes sense mainly because it combines a bunch of features at a decent price--wireless, headset, DH processing. IMHO the wireless aspect is a big selling point (at least it is for me); but for gamers who simply don't need it, please reconsider the purchase.
In any case, if you have both U3 and PLYR1, the only config to avoid is:
DH on U3 > analogue cable > PLYR1
I know, I know. A dumb setup. But I thought it safer just to point it out, as that would be double amping an analogue signal.