First of all the TR-7400 is a business band radio. Even though I have amateur frequencies programmed, It is primary for my security and LE use.
It doesn't matter if it's a "business band" radio, if you're transmitting on amateur or GMRS frequencies, you can't use encryption. Encryption is allowed on business and public safety frequencies.
Secondly I know the frequency that I'm using, but as like any system you have both analog and digital PL's. Those PL's ARE frequencies.
There's no such thing as a digital PL frequency. You have DCS (digital coded squelch) codes or talkgroup IDs, both of which are digitally encoded numbers, not frequencies. CTCSS (Continuous Tone Coded Squelch System) tones are frequencies between 67 and 254 Hz that are mixed with modulated audio, but are completely separate and independent from the RF transmit frequency (somewhere between 400 and 480 MHz). And neither DCS or CTCSS have anything to do with encryption.
Once again, what are you trying to do, and on what frequency are you trying to do it? What system are you trying to communicate with using encryption?