The KPA bypasses your interface's preamp

My guess is SPDIF is a completely Digital system. So the Kemper sound is converted to digital info then sent to your interface. The interface analog preamps are never used because the signal is digital thru the whole process.

Using the OUTPUT jacks means the digital data from the Kemper is converted to analog then sent to the interface. The interface preamps then read the analog data and convert it to digital information.

DIGITAL:

- Preferred method.

- No noise added.

- Signal tone/color/sound is not changed.

ANALOG:

- Tiny distortion added in the Digital -> Analog conversion then Analog -> Digital conversion.

- Noise/Hiss added from the low level analog signals.

- Possible noise added from Ground Loops.

- Signal tone/color/sound is altered by the preamps frequency response.

Most people will not hear the changes in tone from SPDIF to Analog. But some will. And many may hear the added noise.

Ground Loops come from having equipment connected to different power sources and noise that is trying to get to ground travels on the cables connecting these devices. That is why some devices have a Ground Lift switch. Digital data is not affected by this as the GL noise is usually a very small voltage.

Analog noise is present in the world due to the physics of nature. And this noise gets into the analog signal and is amplified by the preamp in your interface. This can just be as simple as noise transmitting from a low frequency light/electronic system near you to a high frequency radio/television/communication signal miles away. So digital only paths are always the better method for noise.

The most important things you want to know:

1. Signal type isn't the same like connection type (and vice versa).

The XLR output of the Profiler is a balanced line level output and it should not be connected to the XLR microphone level inputs of your audio interface. Use XLR female->TRS cables instead. 99.9% of the audio interfaces use the TRS input for line level. The XLR input for microphone level signals goes to the analog preamp section (to be amplified to line level) before it gets converted to digital by an ADC.

2. Balanced audio connections prevent from added noise and ground loops.

Whenever possible, use balanced connections for analog audio. Check your audio gear's tech specs to see whether it supports balanced connections and on which inputs/outputs.

3. Digital Audio and sync.

In your case, there is no ADAT involved at all. If you connect your Profiler via S/PDIF coaxial, you should always use digital cables with RCA male plugs. Do not use regular analog audio RCA cables. Also, always use two of these S/PDIF coax cables. In your interface, you might have to switch the sync source from Internal to S/PDIF ... but this depends on how old your Profiler actually is.

In a digital audio setup there must always be one (and only one) "master", all other connected digital audio devices must be "slaved" to the master. This can be tricky because not all devices allow for external clocking / sync'ing.

Without proper sync, digital audio just won't work. If this is all new to you and you struggle to understand how this works ... stay analog. Much easier to deal with (sometimes).

You can use TS to TS cables to interface. I have had no problems using them. But SPDIF would be the preferred way.

From the manual:

MAIN OUTPUT (1)

These are your main stereo outputs. Use these outputs to connect to a mixing desk in a recording studio, or to the front-of-house mixer in a live situation. These outputs deliver the entire Rig: amp, cabinet, and all effects. You have a choice of XLR (balanced) or quarter-inch TS-jacks (unbalanced). The XLR outputs are protected against 48V phantom power fed by a mixing desk. However, you should avoid feeding phantom power into the PROFILER if you want the best audio quality. Like all inputs and outputs, it offers a ground lift to prevent a loop hum.