I'd recommend looking at Pioneer's web site & download the manuals for all the details, but here are a few major differences:
1. LCD front panel display in the 09
2. More power and up to 10 channels that can be configured differently in the 09:
200 watts/channel X 7 (or 140 watts/channel X 10) in the 09 vs. 140 watts/channel X 7 in the 07.
3. Better video processor in the 09, the Marvell Qdeo vs Faroudja in the 07.
4. Better DAC's in the 09. The 07 uses 6 Wolfson WM8741 DAC's, while the 07 uses the Wolfson WM8740 DAC.
5. SC-09 has 6 HDMI inputs vs. 4 in the SC-07
6. More connectivity in the 09 for example, 6 component video inputs vs. 3 in the 07.
If you need ILink connectivity for legacy universal players that play SACD/DVD-Audio such as Pioneer's 59/79AVi, or Esoteric & some other "hi-end" players, you'll need to go with the 09 which has jitter-free ILink using PQLS.
If you want AC3 RF connection for a legacy laserdisc player that plays Dolby Digital 5.1 laserdiscs, you'll need the 09.
OTOH, the 07 has several things that the 09 won't:
1. Ability to play internet radio in its Home Media Gallery. The 09 substitutes the ability to play networked video files.
2.PQLS over HDMI for jitter-free CD playback. Only CD's though, and have to mate with a Pioneer BDP-51/BDP-05 player to get this.
Both have the same MCACC auto-calibration software, both are Ultra2 Plus certified, and both decode all the new audio codecs, Dolby TrueHD & DTS-Master Audio.
If you want another true flagship to replace & out-perform your 507 (which is supposed to be very musical
), and have the $$ you can't go wrong with the SC-09
OTOH, the 07 will get you pretty close for a lot less $$.
I have no regrets buying the 09 for the money spent, even knowing the 07 was a lot less. If I were shopping now for a flagship or near-flagship AVR or prepro here's how I'd personally rate them:
1. Denon AVP pre-pro + a 7 channel power amp
2. Pioneer SC-09
3. Denon 5308
4. Pioneer SC-07
5. Yamaha RXZ11
If you decide on the 09 or 07 let us know how it goes.