You will absolutely have to use a DirectBox for this. You may also need a transformer to clean up impedance mismatches and noise coming out of the PC. Note that a headphone output from a computer is going to be powered, not line level. If you have a professional audio card in there, then going straight to a DI should be ok, but if not, then you will need the transformer.
Another option would be to send the feed optically if you have an optical output, though consumer optical audio is only rated for about 30ish feet. Not sure how far it actually makes it in the real world though, as I've never personally tried and you would then need a converter for the optical signal on the other end.
You could also use an amp close to the computer to boost the signal and send it to the speakers. It really depends on if you have any other inputs that are needed. Either option should work well, but the key is to minimize the amount of time the signal spends at an unbalanced headphone level and accounting for the mismatch in impedance between consumer and professional gear and the ground noise that comes from poorly isolated consumer audio gear in the computer.