Advice needed! Please help!

[Nikka488]

I'm looking at buying the SR-608 ($449.00 on JR). I'm relatively new to this space (My current receiver is 12 yrs old Kenwood VR-309). I really want to upgrade but also want to spend my money wisely.

The common consensus in this forum is buying separate pieces is the way to go. I would be incredibly grateful if someone would explain to me what benefit there is to me (will I be able to tell a difference) in buying the:

Onkyo TX-SR608 receiver $449 (and say a separate Polk speaker set ~$300)
THX Cert, 100watts x 7
http://www.us.onkyo.com/model.cfm?m=...s=Receiver&p=f

VS.
Onkyo TX-SR508 receiver $299 (and say a seperate Polk speaker set ~$300)
No THX certification, 80watts x 7
http://www.us.onkyo.com/model.cfm?m=...s=Receiver&p=i

VS.
OR Just going HTiB

Onkyo HT-S5300 (HTiB) $499.99
130watts x 7
http://www.us.onkyo.com/model.cfm?m=...s=Receiver&p=f

All three choices are HDMI 1.4a (so future proof). I would be so grateful to get some feedback from people who are familiar with these topics. I have no doubt I would not get honest answers to my questions at a retailer.