just purchased a new 1921 for my "old" 876. The 876 was equipped with a ADVIPSERVICESK9 License, is there any way to transfer it to the 1921 (which only has a IPBase License)?
No, you cannot transfer the license. You will need to purchase a new ADVIPSERVICESK9 license for your new router.
There is no ADVIPSERVICESK9 license for the 1921.
Depending on the additional fetaures you require over IPBase, you may need to get either a Sec or Data license or both.
You can use the Cisco Feature Navigator to compare the commands available on various images and platforms.