X-Fi Xtreme gamer two 5.1 devices

I've got a question hopefully someone can help me with. I have an x-fi xtreme gamer sound card with a set of tritton ax51 plugged into the 3.5mm jacks in the card. I am trying to decide what the best way to install speakers to my computer as well. I have considered using 3.5mm y splitters so I can connect 5.1 channel logitech speakers as well but am concerned that this may reduce quality and may damage components. Also not sure if this will play audio through speakers and headphones at the same time? What about usb speakers?? I do alot of gaming and I haven't been able to find usb speakers that do the surround like a 5.1 channel would.I have read that when you install usb speakers it disables the headphones. Not sure what to do? Thanks for the help!