Configure Accounting setting for Remote Access data logging

I'm currently using inbox accounting on the Windows Server 2012 R2 DirectAccess servers. As the number of users has ramped up, I've noticed the Windows Internal Database (sqlservr.exe) process is consuming more and more CPU resources.  I thought about switching to RADIUS accounting (just to record connection events).  Has anyone implemented a separate RADIUS server just for accounting of the remote access accounting logs?  If so, which one?  which platform?

Thanks...