Apple Lossless is the best alternative for Apple OS users. It's just like FLAC. AAC can not be high quality as it is still a lossy format. I don't believe iTunes Match supports lossless codec. Even if you have lossless files, it will stream them in AAC format. Bit rate and sample rate allow for a larger frequency range. Everyone's hearing range is different, so it really doesn't matter. Plus, most CDs are produced at 16-Bit/44.1KHz. The other thing to note on why lossless is important for high quality listening is because of the fact that it is CD-quality sound.
The best thing to do in order to not lose any quality is to use lossless files and use an external DAC. What's your budget? Are you planning on using a home theater system with this setup? Or just the computer? One company to look into for desktop speakers is Audioengine. They are known for the famous A5/A5+ speakers. Pair it with the Audioengine D1 and you are good to go.
www.audioengineusa.com
The A2s are great, but aren't exactly on par with the A5 series. These both have decent amount of bass. If not, you can always grab the S8 subwoofer later on down the line.
Another thing you can do if you wish to stick to iTunes and not steal another $100 bucks out of your wallet for another music playback interface is to purchase and download an app from the App Store called BitPerfect.
http://www.headfonia.com/tim-murisons-bitperfect-for-osx/
Hope this helps; cheers!