We have devices at client sites that connect to processes on our servers and provide several streams of TCP data. We currently use VPNs to gain security and be able to connect back to the devices, which run embedded Linux, to administer them. We would like to explore other, less configuration intensive ways for them to connect. Is SSH a good alternative? Are there others? Is there a way to set up ssl enabled TCP connections like pop, imap and smtp? Are there other alternatives? Thanks.
It really does depend on what your connections are actually doing, you don't say, but most if not all modern usage cases for IP now have SSL/TLS secured equivalents that may be of use to you.
For instance; SSH instead of Telnet, HTTPS instead of HHTP, SFTP instead of FTP etc. But you need to let us know what you're currently doing before we can respond specifically.