The HT3's woofer can be astounding in the bass department, but in my opinion it needs to be controlled, and this can be pretty difficult to accomplish depending on the system and synergy involved. My advice is to not compromise when it comes to powering the HT3's. An integrated is a handy solution, but please be sure to go "all out" if you can, as the HT3 deserves it and will truly reward you when this is accomplished.
I don't have any recommendations regarding an integrated piece; I'm sorry about that. I just felt it was necessary to ensure you know how important woofer control is when it comes to the HT3. Personally, I'd go the power amp and passive preamp route you mentioned.