1) No, you don't need one. But, if you like listening to music and watching movies, you'll probably want one. The woofers used in a speaker are usually much smaller and cannot play as deeply as woofers used in subwoofers. There are very, very few speakers that wouldn't benefit from a subwoofer. There are other benefits of using a self-powered subwoofer, including less stress on the receiver because it doesn't have to amplify the lowest of bass information.
2) Yamaha generally matches up well with Klipsch. Some other brands that many on here use are Harman/Kardon, Denon and Onkyo.
3) No comparison. Well, I shouldn't say that. They both reproduce sound. That's about the only thing that they share. Klipsch speakers are much more dynamic, much more detailed than almost any other speaker in the same price range. They are also much more efficient and play much louder than other speakers given the same amount of wattage that an amplifier is putting out. Its too bad that you can't perform an A/B test between Bose and Klipsch. You would be shocked at the difference.
**Cables for sale!** ---------> http://forums.klipsch.com/forums/t/121347.aspx-
Mark--1992 Oak Oil
Klipsch forté IIs with Bob Crites (BEC) networks & titanium diaphragms
---1994 Medium Oak
Klipsch KG 3.5 surrounds
----Twin
SVS CS-Ultras
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Samson S1000 pro amp
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Marantz SR7001 THX Select2 receiver
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Dyna FM-1 tube powered FM tuner
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Sony PlayStation 3 (60gig)
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Nintendo Wii----------
JVC 56" 1080p LCoS HDTV -
HD-56FN97-----------
Klipsch ProMedia 2.0 in the office