So you payed way too much for a sound card and now want to skimp on the speakers?! The speakers are the most important part of an audio system.
50.00 speakers will sound below average even on a cheap sound card. You would have been better off spending the 200.00 on better speakers and skipped the sound card altogether.
To answer your question, both will work with that sound card but you won't notice any difference in quality of sound with those speaker choices.
Happy listening, the Prisoner...
Respectfully, it is not the speakers that are the most important. The sound card, or what is producing the sound is far more important and the Xonar Phoebus solo is a very good card. In fact, if one would like, the op amps can be swapped out to achieve a somewhat different sound which many find pleasing to their ears. Call it, op amp 'rolling.' You know, like tube rolling. Maybe a warmer sound or a more neutral sound, depending on the op amp selected. Op amps can be purchased conveniently off fleabay. On board audio is often good enough and lately, mfg's are taking into account the quality of the on board sound for an even better audio experience. However, for the audio enthusiast, a sound card is the better option. Perhaps the poster can only afford "cheap" speakers for now and plans on upgrading in the future? I know I did this several times with my pc and now use home theater speakers(not towers) with a pc compatible powered bass, instead of the plastic 'pc' speakers I was using previously. So, in short, great sound card but higher quality speakers would better take advantage of the sound card's potential.