Time to Upgrade
The Bose cubes are designed to work with the Acoustimass subwoofer, not to be connected directly to an A/V receiver. I couldn't find the manual for the Lifestyle 12, but the manual for the Acoustimass 10 system includes the following warning: "Connecting the small speakers to a receiver can result in damage to your system and possible electric shock." As I was looking around the Bose site, a representative appeared in a chat window, so I asked him if the Lifestyle 12 speakers can be connected directly to an AVR, and he said no. And even if you could connect them directly to an AVR, I'm willing to bet they wouldn't sound very good at all.
I'd start fresh with a good home theater in a box, such as the Onkyo HT-S9300THX (list price $1099, shown above and reviewed here) or its successor, the HT-S9400THX, which we haven't yet reviewed. These particular systems do not come with a disc player, so you'll need to budget for one. I'd get a Blu-ray player, which cost as little as $100 or so, and virtually all of them perform very well.
If you have an A/V question, please send it to firstname.lastname@example.org.