...Yes, a 'receiver' is a generic term for a "home theater audio-receiver
." I've got 5.1 surround sound system, as do a lot of other guys on these forums - some have 6.1, and even 7.1, but the only one that's recommended is 5.1, because every
DVD and Bluray supports true 5.1 surround sound.
But if you want to start small, investing in a 2.1 system (with just 2 speakers and 1 sub) is going to be infinitely better than the G20's awful built in speakers.
...I'm not versed on the audio input options of the G20, but it's not a big deal since a small PC speaker system like this 2.1 Klipsch system from Amazon
will greatly increase your viewing pleasure. ...I've got that exact speaker system setup on my Panasonic 800u, and I can say it adds a lot of immersion into everything done on that TV. After all, audio is a huge part of what makes any viewing experience more immersive.
To properly connect those Klipsch speakers to my TV I just needed 1 or 2 extra connectors to split the PC audio cable into the red/white audio cables, and it worked great. Although these speakers don't have a digital Optical Cable input (to take HQ audio from the PS3/Xbox), I'm sure there are newer PC speakers that have that an option.
So in summation, you've got 2 options:
#1 you can either invest approx $200 in a decent 5.1 receiver, and an additional $300 on 5 small surround sound speakers and 1 sub, or...
#2 just spend approx $250 on a PC speaker system and do what I'm doing above.
...For the record, I've got both setups, my Panny 800u is using the PC speakers, and my Pio 500m is using a 5.1 receiver. And might I strongly recommend that if you're a fan of FPS gaming (like Call of Duty) then def go with the receiver + 5.1 system, because gaming with 5.1 is way cool; plus Bluray movies with 5.1 is a nice bonus (but it really matters when gaming more than movies IMO).