Here's my take.
Hey Mike,
That's a good one from you. These two receivers are quite similar in their category and price range.
You are right, the 2309ci does not have preouts. But the 706 does.
* The Denon 2309ci has Audyssey MultEQ (6 mic positions), 4 HDMI inputs and 1 out.
The list price is $849, and it weights about 30 lbs.
It also has Audyssey Dynamic EQ and Dynamic Volume.
The Dac is an 8-channel Dac (one chip), the Burr-Brown TI DSD-1608.
The DSP is an Analog Devices Sharc 32-bit floating point DSP chip. I believe that there are two of them.
* The Onkyo TX-SR706 has Audyssey MultEQ (6 mic positions), same as the Denon 2309. The 706 has also 4 HDMI inputs and 1 output, again, same as the Denon 2309.
The list price is $899, and it weights about 27 lbs. (Actually, the Denon 2309 and the Onkyo 706 weight pretty much the same weight, when put on an accurate scale).
The Dac in the 706 is the Cirrus Logic Crystal CS-42528, an 8-channel Dac in one chip.
The DSP is the Texas Instruments Aureus, there are two of them, both 32-bit floating point quantization DSP chip devices.
And like I said, there are preouts for all channels.
And the 706 is THX Select2 Plus certified and it has THX Volume Plus and Audyssey Dynamic volume, but not Audyssey Dynamic EQ.
Looks: that's a personal preference, it's your call (but sound quality is not affected, of course).
* And also don't forget which one's got the nicest butt (rear).
Street price: I know that you can get the 706 for less than $500. The 2309ci, I don't know, but my guess is that it is a bit more.
Value (street): I'll say the Onkyo.
*** Conclusion *** Now! The big question, which one should you pick?
Well, you are already acquainted with the Denon sound from your present AVR-2307.
My best suggestion to you, is to get the Onkyo 706, install it in your system, try it for a couple of weeks or so, to get acquainted, try Audyssey, and see if you like it better than your 2307. If yes, just keep it. If no, just return it, and get the Denon 2309ci. No two ways about it, very simple. Life couldn't be better.
Cheers,
Bob
Note: I see that you just edited your post to add some extra info.
Again, the look, it's your call (for me, they both look fine, perhaps with the Denon taking the edge).
The Onkyo have a nice and simple remote (better than the Denon, in my book).
Reliability: Denon is not a problem (I own the 3805). Onkyo, I cannot say yet as it is less than a year that I got mine (805).
If you did follow the thread between Gamblet and myself, you'll see that Gamblet made the right move by getting the older Onkyo TX-SR705. It's all in there, in that thread.
The Onkyos have OSD through their HDMI output (including the 706 & the 705).
Volume display overlaid on your screen display? LOL, that's a good one. I just don't know, as I never use on-screen-display anyway, I always turn that feature OFF on all my receivers.
Besides, in the Onkyo receivers, it is recommended to turn the Immediate Display OFF, by THX recommendation, and I totally agree. But if you like to use that feature (bad for impurities), I'm sure someone will let you know quite soon.
Again, which one is the better one? Very easy answer; the one that pleases you the most.
Just like I suggested you in my conclusion. But now I'm throwing the Onkyo TX-SR705 into the equation (but remember, the upscaling on the 705 is up to 720p; but then it does pass through 1080p in pristine form, which the 706 altered by affecting WbW and BaB, below White & above Black).
Having fun yet?