Klipsch sells stuff in bundles standard rather than individual pieces. If you want seperate parts, they make you pay through the nose for it.
Such as their RSX series of "bookshelf sats", they aren't that expensive in a bundle by a pair they can cost quite a bit ($260 for just a pair of the 3s, $300 for the 4s, $350 for the 5s; midrange drivers at 3.5", 4", and 5")
The Quintet's are designed similar to the Promedia satellites although they have 3.5" midranges. By cost alone you can tell they are not in the same bracket as the RSX series. I'm not sure but I'm fairly sure that there are no sonic differences between the IIs and IIIs, although they aren't as wall-mount friendly anymore.
The RW-8 sub and the iFi subs are different animals. The RW series and up (RSW) use aluminum cone drivers (which they prominently display for front firing purposes, and color them gold). Klipsch's other lines are down-firing poly drivers (KSW, Sub-, KW). The iFi sub has a front-firing driver but I believe it's a poly one that's been colored silver. Owners of iFi's have said it's basically a 5.1 sub with less port noise, so it's not quite there with the RW-8 in clarity yet but extension should be comparable (since the RW-8s are really dinky sized rectangular subs, decoupled from the floor and front firing). But still, to move up to say the RW-8 most of the price ($300) would be for the "Klipsch" decor. It definitely can't compete with many of the budget subs these days in extension (dives at 32hz, versus say 25 for other designs due to driver and enclosure size ) or SPL. (examples: Hsu STF-1, Bic Acoustic H-100, Dayton Sub-120, Polk CSW10)
Edit: morkus64, good luck on your new speakers. You'll find as you get bigger and bigger speakers the soundstage will increase, distortion decrease, and the sound will be fuller. Lower bitrage songs will be less and less acceptable : )