I'm not familiar with the "made by Denon" you speak of. If you want to drive them with a receiver, it needs to be a "high-current" receiver. Denon makes high-current receivers, as do others, like B&K. From the specs posted on Denon's site, your 2807 appears to a high-current model capable of driving 4 ohm speakers. You don't NEED separates, but you may find an improvement in sound if you use them. I'm mighty happy with just my B&K driving them, so choose what matters (and sounds best) to you. I called B&K to verify my AVR would drive 4 ohm speakers. You may do the same with whatever receiver you plan to purchase--call the mfr tech support and ask if it will drive 4 ohm speakers.