As far as i know, you can't sync a windows 8 phone's music to windows 7. You can sync WP8 to Windows 8 (with xbox music) or WP7 to Windows 7 (with Zune). But, I could be wrong, this is just from my attempt at syncing.
There are several issues with WP8 and syncing music. They basically did away with SYNC and are in the proces of launching "Cloud Music/Sync". Again, the cloud sync doesnt yet work.
Check out this thread that may help you.http://answers.microsoft.com/en-us/winphone/forum/wp8-wpmusic/master-list-of-issues-with-xbox-music-...
The best way to "sync" music at this point is to use Windows Media Player and setup a sync partnership through it. I havent done that but read in other forums that many have found this method useful until MS fixes Xbox Music.
Check out www.wpcentral.com for insights into WP.
Also, regarding the Win7 OS that you are using. The DRM between Zune (or what was Zune) and Xbox Music are totally different and cuase playback issues. If you have a Music Pass. your best bet at this point is to just download songs directly to the Phone with your pass. Use WMP to "sync your DRM free music, or just drag those tunes to your Music folder of the phone in My Computer.