Just wanted to know is it worth bi-amping Klipsch RF 62 II- because i am planning to buy a receiver with extra two channels (2 amps) especially for bi-amping purpose.
The Laws of Physics aren't swayed by opinion.
I do think passive bi-amping is worth it. I wouldn't bother for the HT, for but Hi-Fi it is.
Then what is the use of subwoofers in the front towers when i have a good sub or both sub woofer can be used? for example RF62 II can go up to 35Hz and if my sub goes down to 20Hz can i still make use of the subwoofers in RF62?.
They're not subwoofers they'r woofers. Not many floorstanders have subwoofers in them, some Definitive Technology. I use Kef Reference and the bass drivers in them aren't equal to a sub, however for stereo I do prefer larger mains, rather than standmounts + subwoofer. Although it depends on the the room, and the setup. Small room = small speakers. However other things to consider can alter crossover frequency, or are you sending full range. Or do you run high pass so able to filter out low bass from speakers. When running full range what is like in that room? Too boom? Then use a crossover, with a sub to bring up low end but not so much as floorstanders in a small room. When you listen to music (large room) do you prefer floorstanders with no sub?
Budget too. And what amplifiers you are using. It's not really a simple answer that one is better than the other.
btw I use floorstanders + sub in the HT. And standmounts + sub in the Hi-Fi.
Some people prefer using THX style speakers in the HT. It's all down to taste.
Best to play it safe and set those as small and crossed at 40Hz or 60Hz whichever sounds better to you. Let your outboard subwoofer do the heavy lifting of the lower frequencies.
Just in case you can't quite visualise what is going on yet... understand those speakers are only 2-ways. The crossover is 1500hz from the two woofers to the horn tweeter. The two woofers (acting as one) cover everything from 1500hz down. The horn, everything from 1500hz and up.
So taking 60 or 80hz off the two woofers and sending that to subs is still leaving 60 or 80hz and up all the way to 1500hz to the woofers.
You get two benefits from doing that. Better coverage from say 80hz down, and better midrange clarity because of the midrange drivers being relieved of the very low bass duties. It's a win win.