The short answer is yes, you can split your music collection over 2 drives. But I think in your case that might not be the optimal decision, as it sounds like it would interfere with your backup mechanism at the moment.
Better would be to get a 2 TB drive and either a 3 or 4 TB drive. You can likely just take the drive itself and install into the existing enclosures by unscrewing a few screws and replacing the existing drives.
Copy one of the 1 TB drives into the 2 TB drives. Then make the larger (3 or 4 TB) drives the Time Machine, and ensure that it backs up the external drive. The difference is that this will give you a more complete backup and allow you to recover from deleted files, viruses, mistakes in tagging, etc. I also recommend an online backup service to guard against theft and fire
Michael
Better would be to get a 2 TB drive and either a 3 or 4 TB drive. You can likely just take the drive itself and install into the existing enclosures by unscrewing a few screws and replacing the existing drives.
Copy one of the 1 TB drives into the 2 TB drives. Then make the larger (3 or 4 TB) drives the Time Machine, and ensure that it backs up the external drive. The difference is that this will give you a more complete backup and allow you to recover from deleted files, viruses, mistakes in tagging, etc. I also recommend an online backup service to guard against theft and fire
Michael