I suspect the problem may be with how you are streaming music wirelessly to your av receiver. Try a direct connection (rather than a wireless one) and connect a computer, an iPod, or a hard disc (the AV receiver I believe from the specs supports this,
Products) and see what happens with your apple lossless files. Apple lossless is, I think, a good format and iTunes a good interface; I wouldn't give up on it so quickly.
I would do some research and google around. There may be some software solutions to help you out if you wish to stick with iTunes and DNLA.