i want to state i dont own the xb1000 or the dacmagic+, just so theres no mistake.
does the dacmagic even have an amp? if its just a dac, it makes sense that you dont have enough volume i guess. but if it does, then i dont really know... to be honest, i think bass boosting amps are usually portable options - like the fiio e11, cmoy amps, zo2 etc. i dont feel comfortable recommending an amp as i only own 2 portable ones and i havnt enough knowledge or experience to do so. i suggest using the sites search option.
for all i know ther may be full sized amps that offer a bass booster too but why not just use an equalizer? do you use foobar?
as for not hearing any difference in sq. what was your source before? according to the specs i read briefly, the dacmagic uses dual wolfson chips, which sounds pretty good to me... im currently in the market for something alot less impressive, but i have a laptop, which means my sound card is probably not all that good. perhaps the sound card you had was already of good quality?
i feel like im searching in the dark really. like i said, i havnt enough experience to answer these questions. if you use foobar i can recommend an equalizer and explain how to install it, more than that - search the forum, im sure youll find what your looking for.
just thought of something though, im guessing your playing files off your computer? set the volume on 80% and use the dacmagics volume control. if your not doing this already, this may be the cause.