Balanced Amp

The TRS connection is apparently just those big phono style connectors. You could very easily get a 3.5mm to 6.35mm TRS connector for the PC.

The sound should be fine as I think they are made to be used for desktop style use in a smaller room.

I doubt very much you will need an amp to power them. I would say he invests in a good audio sound card though if he hasn't got one already.

Something like this:

http://www.scan.co.uk/products/scan-audio-adaptor-35mm-trs-jack-%28female%29-to-63mm-trs-jack-%28male%29

That adaptor is for headphones. While the TRS socket is just a large headphone plug, the wiring is for one speaker (one channel) not two channels like a headphone plug or socket. 

A TRS to RCA adaptor might work. However, it crosses the "-" with the ground channel, which may or may not cause issues. 

For these kinds of things, I bought an XLR to RCA adaptor that could be modified and removed the connection in it between the "-" and the ground as recommended for the gear I used. 

If your friend knows someone who can do a little DIY work for him, have him get a pair of CineMag CMLI-15/15B transformers (http://www.cinemag.biz/) and wire them up as per the illustration on the right in this application note:

http://jensentransformers.com/as/as060.pdf

Note that in this application, the transformer's primary is used as the secondary and vice versa.

The adapter should be located as close to the speakers as possible. Two transformers, a couple of project boxes and some connectors should cost less than $200. 

It offers excellent performance as well as providing ground isolation between the computer and the amplifiers in the speakers.

Whichever route you choose, good luck!

se