The Yamaha will give you real world figures of somewhere between 42 and 47 watts per channel with all 7 speakers going, that is actually typical for receivers in this price bracket, the figures they usually quote are for 1 or 2 channel driven.
I like the Aventage range but my experiences are with the higher priced ones of which i own one, not sure of the lower priced ones but they should be okay, i couldn't say if they are better than the ones you list, my advice is Google them all for reviews, don't just read one review, read many and read between the lines and try and get in the reviewers head, not all reviews are accurate but if you can read many reviews and all say the same thing it is a starting point, then read the forums and owners opinions and if a consensus is reached you make a decision.
I personally think calibration and working on speaker placement and room modes can get you much better sound than just buying a receiver and hooking up speakers and thinking the work is done, sound and room interaction with that sound play a huge part in home cinema.
Looking at your list, if it was me, i'd probably buy the Marantz 6007, they are tuned slightly different to Denon even though they share the same design and innards.
The Sherwood had a lot of problems when it was released but apparently those issues are all fixed now with firmware updates, it also has Trinnov 3D sound calibration, i hear good things about this, might be worth considering if very good sound quality is all you want in a receiver.
Small speakers in a big room, well you could try a couple of decent subwoofers and also place the speakers nearer to you, this can cure some room mode issues, it's really a case of experimenting and you could use something like this, link below, to really make your sound much better, it will require additional equipment, i'll go so far as to say that room calibration could enhance your sound so much you will think you have a brand new receiver without needing to buy one.
The receiver will have sound calibration built in via a mic you hook up, it might be YPAO or Audyssey MultEQ XT or Audyssey MultEQ XT 32 or Trinnov or Pioneers MCACC, they do a decent job but i don't think they are as good as doing it manually yourself, i found the higher frequencies were lost with YPAO calibration and preferred tweaking the settings myself, i let the auto calibration do the speaker distances, it gets the subwoofer spot on because it takes into account reflections before the sub hits your listening position, other than that i prefer manual calibration using equipment and discs i own.
Edited by FoxyMulder, August 20 2013 - 02:27 AM.