OK. First and foremost, people always recommend what they own most of the time. The most important thing to do is go listen. Your ears are most important. That being said, here is my opinion on what you have mentioned:
I am not a fan of Onkyo. I was not impressed with their receiver I auditioned a few years ago. I think their reliability is questionable. I prefer Denon. To each their own...
Polks to me are budget speakers. I have heard the tsi and rti lines. I have not heard the lsi. They are OK, but not the best bet for the money.
I have never heard cerwin vegas.
Klipsch hurts my ears. Too harsh for me. Others love them. I have auditioned the RF lines and they just weren't for me. You would have to listen for yourself and make that decision.
Energy makes some good speakers but I would stick with the Veritas or RC lines.
I have not heard Aperion but they seem well reviewed and offer a free in home trial with paid shipping both ways so you have nothing to lose. Give it a shot.
I own Paradigm monitors because I loved their sound compared to everything else I had available locally. For me they are equally as good for theater and music for what I paid. I run v6 monitor 9s, CC290 center and mini monitor surrounds with a Hsu sub. I like it, others may not. Paradigms are not sold online. Only local dealers so price varies. If interested, you would need to go audition them.
Just a starting point:
Acsend CMT-340 plus the matching center $950ishhttp://www.ascendacoustics.com/pages...m/cmt340m.html
CB-170 surrounds $375http://www.ascendacoustics.com/pages...70/cbm170.html
Hsu VTF-15 $1000http://www.hsuresearch.com/products/vtf-15h.html
Pair it with a Denon 2112 from Electronics Expo for $450
or the 3312 for $799 (call in prices) and you should have an exceptional system for HT and music.
Thats about $3000 (give or take a few hundred depending on your choices)
As a side note, Paradigm monitors run $1500-$3000 roughly for the speakers (L/R/C/surr) depending on the models you choose. If you go to the studio or signature line they are significantly more. With a decent sub and receiver it will still bring you in under your $5000 budget.
Good luck and enjoy the experience. I personally love shopping for audio equipment.