When you say you can "turn the router on successfully", do you mean using the solid-state relay outputs on the PMDX-107? Or are you using something else to turn on the router (like one of the PMDX-126's relays)?
What are the PMDX-107 DIP switch settings? What are the PMDX-126 DIP switch settings?
For speed control you need to tell UCCNC to output a PWM signal on pin 16 of whatever parallel power is connected to the PMDX-126's primary parallel port. As I recall PMD usually recommends a PWM frequency of 100 Hz, though the specs on the PMDX-107 allow a range of frequencies. I've never used or even looked at UCCNC so I have no suggestions there. Try their forums if you don't know how to configure a PWM output. There is a PWM LED on the PMDX-107 that should glow brighter or dimmer depending on the PWM duty cycle.
Depending on the PMDX-107 DIP switch settings, you may also need the PMDX-126 to generate a "charge pump OK" signal.
As I recall, the PMDX-107 won't turn on either of its solid-state relays (or the LED indicators for them) unless is sees the "charge pump OK" signal (or is configured to ignore it) and it sees a valid PWM signal.