the schiit modi and magni dac/amp combo ($99+109) is great for the low price and is what is suggested by even audiophiles over at head-fi for headphones. it plugs in via usb and specifically is made for the purpose of such headphones. likely this will be the best quality you will get for cheap but its not going to support speakers (you would need to use your pc soundcard for those)
if you wanted 5.1 sound capability for speakers then the cheapest you could go for a soundcard which can power 250ohm headphones is $99 for a creative soundblaster z. i wouldnt rely on it for virtual surround though as it is capable but SBX sounds like crap compared to the other options.
if you wanted better virtual surround then i would go with the...