Does Home Sharing serve the original quality file?

Upgraded my lap top to a macbook air recently and just realised the headphone jack doesn't double up as a toslink optical output. Thanks apple - would have paid extra if it was an option.

I used my old MacBook pro to serve a lossless Music collection via the optical out to a quality DAC and onto the amp.

I just tried using a USB hub on the MacBook air to output the same digital signal to a DAC that accepts a USB input, but the quality was *****. Presumably the hub was the culprit.

So one option is using the old MacBook pro, home sharing my library from the new macbook air - but are the files homeshared in the same format, or does the computer automatically downgrade them to serve across the network??

So annoying. Nick