I have, well will have again, a Denon AVR-3300. As you may have read, mine is not working properly, but have been told I will get a new one. Anyway, I will quote what the owners manual says, and then ask my question.

"For Future Multi-Channel audio format(s), the AVR-3300 is provided with 7.1 channel (seven main channels, plus one low frequency effects channel) inputs, along with a full set of 7.1 channel pre-amp outputs, controlled by the 8 channel master volume control. This assures future upgrade possibilities for any future multi-channel sound formats."

This leads to my question. Does anyone know of or had these upgrades done? Does this mean with this reciever, I could possibly have it sent to Denon for an upgrade to make this 6.1 or 7.1? I know it is 5.1 capable now.
Thanks, Oak

Oak, by the sounds of it that Denon is already a 6.1 or 7.1. What it is telling you is that the 6th and 7th channels have 'pre-outs' so you can setup those extra speakers.
However, those extra speakers would need separate amps to power them. Your Denon probably only powers 5 internally at the present time.

Time to show my ignorance

When adding an additional amp to a receiver so that you can go from 5.1 to 7.1 can you set it up so that the newer amp (in this example lets say it has more power per channel than the original receiver) can power the left & right mains instead of the back surrounds?

You can add a new amp (or use a different amp to be more precise), to power any speaker channel that has a pre-amp 'line out' connection on the back of your receiver.
Most people who have a self powered (integrated amp) subwoofer are already using one of these pre-out lines with an RCA cable to hook up their sub. In the same way, you would use an RCA line (or XLR balanced connection which most a/v receivers do not have) to add that new amp.
If you have a pre-out line setup for your front speakers on the back of your receiver, then yes, you could use a completely different amp to power your front left and right as opposed to surrounds.

Yes you could, but you would still need another separate amp to power the back surrounds, as their is not an internal amplification source built in to the receiver for the backs.

That's not necessarily true. Some 5.1 receivers allow you to assign the amplifier to any channel. You'd then re-assign the amps to the rear and use the new stereo amp to drive the front speakers through the pre-outs.

However, I have no idea whether or not the 3300 is such an animal. RTFM.

I think you also you need an external DD DTS decoder 7.1 capable. The one built-in in the Denon AVR3300 is only 5.1

The receiver just has the 7.1 'pre-ins' & 'pre-outs' to hook up the external decoder.