Let me try to address a few of your concerns:
1) Sound differences between RX-V2400 and RX-V2500
This was an impossible test for us since different people reviewed the two products in question and are not co-located, nor did we have both samples at the same time to do this comparision.
To make an educated guess, I would say the sound differences between these two units is minimal. They are very similar to each other and if you already own an RX-V2400, why on earth would you want to sell it at a loss in favor of the newer model which is very similar in performance and features?
Upgrading from the RX-2400 to the 2500 only makes sense if the features listed in our
matrix are essential for your application.
2) Sound comparision between the Denon AVR-3805 vs the Yamaha RX-V2500
This was an impossible test for us since we have both samples at the same time to do this comparision. Would you have us rely on memory from over 5 months ago to declare a sonic winner?
It is best to compare the two units for yourself based on what features listed in our feature matrix at the end of each respected review are important to you. At this price point, sonic differences between models may exist, but are usually subtle for leading competitors such as the two in question.
Personally I prefer the bass management features of the AVR-3805, and active Dlink.
On the other hand, I prefer the DSP modes of the RX-v2500, user interface, and auto set-up.
Is there a declarative winner? It depends on what's important to you. We provide the info on the products, the pro's and con's, tour of the operation, objective measurements (when possible) and our subjective experience with the products. You decide on your own which product(s) fit your budget, requirements and preferences.