Hello Spencer,
The comment you saw was correct, the VPN on a SPA525 will not work with your prosafe.
The SPA525s VPN uses SSL VPN. You would need a device that supports SSL VPN. I looked over the manual for the Prosafe and it looks like it only supports client-to-gateway connections using VPN client software.
According to the admin guide a UC520, ASA5500, or a 500 series secure router are the supported options for SSL VPN.
There are a few other Small Business Devices that offer SSL VPN, for example the ISA or SA series security devices.
Christopher Ebert
Network Support Engineer - Cisco Small Business Support Center