I suppose it depends what you can pick up a 2700 for.
I have to admit to not hearing a 2600 or a 2700 as the dealership i worked for at the time didn't stock them, but having heard standard DD decoded by a 3800 compared to a 2400, it seems clearer and more 'airy', to coin a phrase. Personally I'd rather bitstream out HD codecs and have the amplifier decode them, as a decent quality amp will have a better decoder than something like a PS3, and there's no conversion of any kind in the player. Some may say that BD players will decode better, but I'm basing this on the assumption that the majority are going to go for budget BD players, whose decoders obviously won't be quite as good.
So to sum that one up, if you're gong for a high quality BD player, a 2700 will do the job just fine. But if a budget player is destined for your rack, go for the 3800.
On paper, many of these amps will appear the same, but in practise is where the differences creep out. It's like saying that a Denon 4308 is almost identical to a Denon AVCA1HD......okay, maybe a slightly exagerated comparison, but hopefully proves my point.
Any speaker system can only sound as good as the amplifier allows them to, which is something many overlook, and then complain their system is lacking.