hi vinay
with your longish write up it seems you are in for a compromise after having spent a fortune for your HT set up
The size of a movie in a BD (50GB disc) varies from 30-40gb with out any extras, so to ask if there is an improvement by 10 -15% in a downloaded rip size of 8-10GB is

would like to know if a BD rip of 8-10gb has HD audio? (8-10gb is the size of the HD audio itself in an original)
A rip size of 8-10gb is beyond 50% compression, after having spent so much of money and time on your HT why ?????? are you hell bent on compromising on Quality . These rips may be fine upto 40"-50" displays
Vinay ,you also need to upgrade to HD audio, with your kind of set up you need to get the best of Audio n Video
The route you could take
1) I do understand its impossible to buy BD discs regularly
2) invest on a BD drive 50-100$ (u already have the media player and HDD)
3) Join a rental Library ( you dont have to play the BD on your BDP you only have to play on your BD drive for abt 45 mins) i suppose there wudnt be any cross infections:lol:
4) Most rentals have door delivery and pick up
5) Get ready to Rip -store - transfer to HDD -watch ,rest u decide what u want to do with it. (v shall guide you on this above process)
this is the most simple way for you to get the best out of your investment you would be owning an original BD rip for the price of your rental :lol:
When there is scope for improvment be it 10-15% , IMO way beyond why not give it a shot.
In between ,occasionally if you are in love with a movie you could consider buying the BD