Any ".1" system is simply out of the question without a proper digital decoder. He will get 2 channel, or 2 channel played over 5 speakers (maybe including the sub).
Depends on his TV model, but the TV won't have a dedicated subwoofer channel. The spliter you linked may or may not redirect a signal to the sub. However if it does, it will be playing the same frequency range of the other speakers. The speakers will be playing bass they aren't design for, and the sub would be playing mids and highs it isn't designed for. There would be no cross over point either, so it will sound like crap. Speakers playing the frequencies they weren't designed for won't hurt them, but it will tax the built in amp, and also sound like shit.
The only way he can preserve the bass channel or surround, is to have a proper digital decoder of some sort (i.e. AV receiver). Also an entry level receiver wouldn't even help him since they will usually only have left/right outputs and one for the sub only. You would probably need an $800 model for full analogue outs. Other than that, he can chop the connectors off of each speaker's wire, and use the traditional bare wire outputs on the receiver lol.
Also he won't get 'good' bass with a speaker system like that anyway. The have a good rating for computer speakers, but computer speakers fall waaayyyyy short of home theatre standards. And when I say home theatre standards, I am not meaning spending thousands on a setup. They just know what features and performance to look for, and an idea of what price ranges should have what specs.
His speaker system only goes down to 50hz, which I assume is specific for subwoofer's limitation. Now I can't find a frequency response curve for it, but either way 50hz falls short for a sub. 30hz is good, and 20-25hz is recommended for a home theatre sub for getting the full experience from action movies.
Anyway, You get what you pay for and I think your friend needs some perspective to understand what he will get for what price range:
I recently did some shopping for a 5.1 system for my computer, and there is just no high end units for PC out there. I used to have a Logitec 7.1 system, that even years later is decently reviewed, but I was unhappy with those from day 1. They just seemed under powered. I decided on an av receiver, and unpowered speakers for $500ish. That is about the price you would expect a top end 5.1 system for PC to be, but still falls relatively low in performance to traditional audio system standards.
Anyway I got the Monopirce 10565 speakers: http://www.monoprice.com/Product?c_id=109&cp_id=10906&cs_id=1090601&p_id=10565&seq=1&format=2 and a Yamaha entry level receiver: http://usa.yamaha.com/products/audio-visual/av-receivers-amps/rx/rx-v377_black_u/
The Monoprice speakers are noticeably better than the Logitec ones, but the subwoofer is on a whole nother level. Not just deeper bass, but much cleaner/tighter bass. The receiver adds value too by having software to configure the surrounds to be able to be placed in front of you and still give you a surround sound experience.
What your friend is trying to do is a 'doable/good enough for now" solution, but speakers last for years and years. If he is looking for a good setup, he should consider making the investment. I mean my $500 solution will last at least 10 years, so that is $50 or less a year. And when I say 10 years, that is probably when I decide to do something better. He will probably end up spending $50 or more on all the adapters he would need anyway.