Hey bottomdweller. Glad you "surfaced" to learn more about Basslines Tone Circuits. The models you identified are replacements for Music Man basses.
To answer your question, they both have a master volume; but since Music Man basses are typically single pickup instruments, these circuits don't have a blend control.
If you have a two pickup bass, this is not the Tone Circuit for you. You'd need a standard STC-2 or STC-3. The number refers to the number of bands of EQ. Also, after the number is the letter "a" or "p," which refers to the type of pickups you're using with the the circuit: active or passive.
There's some specs here and a wiring diagram here.