You might want to give this a try:
http://www.amphony.com/products/t800.htm
I recently picked up the 800 transmitter and two 880 wireless amps to provide music/news in the shop without running wires. I can't 100% recommend them for your application because I haven't tested the delay and I do occasionally get brief (like 1/10th second or so) drop outs--usually when walking right up to a speaker and standing in front of it. But in my case they're transmitting about 40 feet through a wall and a couple steel cabinets so I wouldn't expect that under better conditions but I can't be sure.
Anyway, I've been extremely happy with the setup. The sound is crisp and crystal clear. I've used several systems in the past and always had interference noise (buzzing, popping, etc) and there is never any of that with these. The amps appear to be a legit 80 watts and when hooked to good speakers can get very loud.
The transmitter is quite versatile in that it has line-level
and speaker level inputs. This means you can hook it up to any old or low budget AVR that doesn't have pre-outs just like a set (or two sets--it's four channel) of speakers. The systems I've used in the past had headphone jack inputs which are very difficult to use in an application such as yours. And the wireless amps will turn any old speaker into a powered speaker. If you have powered speakers, you can get the wireless receivers instead and save a bit of money.
In any case, while I can't be 100% certain, I do think this system has a very good chance of doing what you want to do very well.