Hi mate,
Just a couple of factors you might want to consider before making a decision. Firstly, what type you sound you like would influence amp recommendation e.g. if you like bright sound which is sound that has greater emphasis on the higher frequenies or treble and can be described and clear, exciting, crisp and sometimes shrill or harsh then the Onkyo would be a good choice (sony is another brand you could go for). If you like warm sound which is sound that has geater emphasis on mid/low range and bass and can be described as rich and full and sometimes muddy or bassy then either yamaha or denon would be a good choice (both also good with music). Neutral sound sits somewhere in the middle.
For speakers it would be worth looking at how much space you have. If you have enough space and/or the room is big enough i would def go for floorstanders. These would sound great with music as well as movies/games. If space is at a premium then getting a sat/sub package or some bookshelf speakers would be your best bet. These type of speakers are generally small and discrete/inoffensive but would not sound terribly great with music and would almost certainly need a sub to go with them.
Then you might want to consider what speaker/amp combination you want to go for. Pairing a bright amp with warm/neutral speakers is a good choice and vice versa.
It really depends on what type of sound you prefer, getting some demos i n would be a great start to help you with deciding too. All the amps you mentioned above are very good amps, you would go wrong with any of them. Also, how many sources will you be connecting? You will need to think about things like inputs/outputs etc...
I've prob thrown up more questions than answers, sorry about that!!
Cheers
Saf
Edit: which denon were you looking at the 1610 or 1910?
Also, of the amps you listed above, the onkyo 607 gives you more flexability around connections but the yamaha is more powerful, and better muscially imo.