There is a very robust solution for Tape Backup called CA ARCserve Backup r15.
It does a good job and the licensing is something that might make it attractive in your case. ARCserve provides some critical techology free of cost as included in the backup base product license including Deduplication, Advanced Dashboard & SRM Reporting, Encryption, Infrastructure Visualization, Disk Staging, etc…
Another good thing is that ARCserve Backup r16 Beta is already out and includes added functionality around Data Archieving. If you make an investing right now, you would be eligible for the free upgrade(under the terms of the maintanence contract) once the new version is out.
There are free 30 day trials on the site in case you decide to have a look: http://bit.ly/gg43wt
Link to the Beta Center to look at the advanced archieving functionality added into the next version: http://bit.ly/gZevEA
In case of questions, let me know right here.