Amp for Denon 4311CI to get the extra 2 channels

Emotiva XPA-2, $709 shipped right now. Use it to power your mains. That's what I do.

Understood.

Emotiva UPA-2. $329 shipped.

Check craigslist, ebay for an Audiosource.

I'm going to power the heights with two unused channels from my HK garage receiver.

Keep in mind that the only way to get power to all 11 channels is either in the 11CH mode(ie using a 2CH amp for either the Front L/R or Front Height and the internal amps for the other 9 channels) or Pre-Amp mode (external amps required for all 11 channels).

If you already get loud enough without an amp, then adding an amp for your front 3 channels won't cause a problem. You will, of course, calibrate the system so that the front 3 are in proper balance with the rest of the system. Then you just have more (presumably) headroom in the important front 3. Plus, you've removed load from the receiver so it should be able to get more clean power to the rest of the chanels, if needed.

I noted in my previous post ... either Front L/R or Front Height. As Noah Katz mentioned he plans on powering the front heights. Depends on how powerful the amp is whether it makes a difference or not to power the front mains. If you're just going to pick up a used 2CH stereo receiver (~$50) then the front heights. If you're going to pick up an EMO XPA-2 then the front mains.

If you are happy with your 1909 power levels then my .02 would be to buy cheap, used 2ch amp off craigslist or eBay and use it for your front heights. Even if it is ugly you can just tuck it out of the way. Later if your speakers require it, you can dump the money into a 2 or 3ch separate to get more power to your fronts.

There are tons of very decent solid state 2 channel amps from 90's style rack systems out there to be found for $20-$50 that will keep up with the 4311 amps just fine. Yamaha and Kenwood are probably the most common, but once you start looking you can find all sorts of H/K's, Adcoms, NAD's, etc. Most of them will be rated in the 75 - 125wpc range and will match the Denon amps just fine. Some of them can be very understated and decent looking, if not just tuck it out of sight.

Just connect an RCA red/white cable from the Front Height pre-outs on the 4311 to the Front L/R EXT IN on the 1909. Then set the 1909 source to EXT IN. Then wire your front heighs to the Front L/R speaker posts on the 1909 and you're good to go. You'll want to run AUTO SETUP on the 4311 each time you add more speakers while building up to the 11 speakers.