I bought The Binding of Isaac together with the soundtrack, and now when I want to download it to another PC, instead of the binary Steam also downloads the soundtrack, increasing the download size. Is there any way to avoid this?
I know this is a rather old question, but for anyone still having this issue:
There is the option to choose which DLC content should be downloaded and installed in the steam beta client. Sign up for the beta, switch you client to beta mode and then under the properties of your game, you can install / uninstall each piece of DLC individually.
Someone with a similar problem contacted Steam support and got the following reply:
"Unfortunately we do not have the ability to remove DLCs from games. Once a DLC is purchased, it is automatically added to the game install files. We understand the inconvenience this may cause."
They gave him the option to remove the DLC from his account, but that was about the best they could do.