Questions about input signal.

[jivex5k]

Forgive me if this is a very basic question, I'm still learning about amps.

I have an RME babyface FS pro as a DAC, my plan is to use the 1/4" TRS stereo output with a Y Cable that converts it to 2 mono male RCAs.
The headphones get pretty loud already if plugged in directly, is it possible to send too much volume and damage the Crack?
The outputs are a line out signal, and I believe as long as I don't send an amped signal it should be fine.

Also, what should I set the volume to on the DAC output?
I'm guessing just start it low and fiddle with both that volume and the crack's volume until I find a good level. I'm probably worrying about this too much...

If interested, here's the specs on the 1/4" output:
    Output: 6.3 mm TRS jack, unbalanced
    Output impedance: 10 Ohm
    Output level at 0 dBFS, 1 kOhm load: +13 dBu
    Max power @ 0.1% THD: 60 mW
    Signal to Noise ratio (SNR): 114.8 dB RMS unweighted, 118 dBA
    Noise level: -101.8 dBu

The interface also has a 1/8" TRS stereo output, and 2 mono XLRs outputs.
I figured there's no point messing with XLR since the headphones I have are unbalanced. (DT1770s)

[Paul Birkeland]

The headphones get pretty loud already if plugged in directly, is it possible to send too much volume and damage the Crack?

There is a signal level that's too much signal for the Crack, but it's the kind of level that you would get out of a big power amp, not another headphone amp.

Also, what should I set the volume to on the DAC output?
I'm guessing just start it low and fiddle with both that volume and the crack's volume until I find a good level. I'm probably worrying about this too much...

I would start all the way up.  Sometimes the channel balance of the pot in the Crack isn't perfectly matched at low levels, and if you run that you can lower the volume from your DAC to get into the upper ranges of the volume pot on the Crack.

+13dBu is a lot of signal, so don't be surprised if you need to turn the level down a fair bit.