> but there is no "Software Playback" in Digital Audio Workstation Mode.

Then use the full mode. You can mimic DAW mode in full mode with a few mouse clicks, see my post here:
https://forum.rme-audio.de/viewtopic.ph … 03#p188003

It is better to use full mode and use routing like DAW mode in full mode, than to limit the routing possibilities of TM FX by the DAW mode where you have to route in the DAW and where you have full RTL (round trip latency) for all audio flows.

It's much more powerful if you can additionally route audio directly on the device, in near real-time.
Ideal for creating submixes where part of the audio comes from computer (backing track) and
other part directly from a HW input (e.g. vocals).

> This means that I can only perform loopback on the original route.

Sorry, do not understand what you mean by this (Original route ? What do you mean by this ?).

Loopback simply enables you to record audio of an HW output on it's corresponding HW input.
If there
- are no SW playback channels or
- is no submix mode
in DAW mode you can stiill enable loopback on a HW output.
You see the Loopback button on each output?

> However, I set the route to -54.6db, which will cause Loopback to be -54.6db, which sounds very silent.

You didn't mention your product. On some recording interfaces loopback is implemented pre-fader,
you seem to have a device where it is implemented as post-fader.
See this request: https://forum.rme-audio.de/viewtopic.ph … 58#p171758
Sadly it turned out that it's not possible to implement it in a way to make it configurable.