Re: Speaking of speakers, can I have your input?
Well, Kristen, I am glad to hear Onkyo is swapping out the receiver. I always insist on replacement when a new item is not working properly, and fortunately often get it.
You have a HUGE volume room, so getting big volume will require efficient speakers, (the higher the efficiency, the louder they will play for a given power output). That said, your room is very large so will take a good deal of output to get the volume you describe, and unless you get lucky on the used market (Audiogon.com is my favorite site for audio gear) you won't get what you want for $600, and definitely won't get a 5.1 system that will do that room any justice.
You mentioned lots of classic rock, desire for high volume, and smooth sound, and if theirs one speaker that fills that bill, it's the new Definitive Technologies Mythos ST. I bought my review sample and still have them rocking the HT, Stereophile just raved about their baby brother, the STS in this months issue as well. OK, the down side, the retail for $4K (ST's) or $3K (STS's) a pair, the STS's sound virtually identical tothe ST's, they just put out less volume, so if you could swing it, a pair of ST's would be a great match for you, they are efficient (93db), can play louder than you should ever listen to (I clocked >110 db in my room of similar size) and they have powered subwoofers built into each speaker so bass kicks a$$. They can often be found for less than $3K new, so I assume the STS's can be has for sub $2K if you shop hard, maybe better if someone is selling used ones but they don't last long on the market so if you see them, make the deal fast or they'll be gone.
I know it's more than you currently budgeted, but to be honest for $600, your not going to be happy with what you'll get, and they anything you can get for that won't do the room size well or sound very good......
I know, I am once again encouraging someone to go beyond their anticipated budget, but FWIW I always seem to do this myself too!
Ken Taraszka, MD