I need to share user accounts of main site with buddypress

Hi, This is my first post and I really love wordpress. I need a help, Is there any solution for using same user accounts of the main site for buddypress accounts.(Actually I have a premium theme for main site. I don’t want to convert it into anyother theme(supported by buddypress). Thats why I have installed buddypress on a separate wordpress installation.
I just need buddypress features for my main site.

here is my main site. open houses in boston and its buddypress community site address is buddypress community site
all suggestions are welcomeو
thank you