Can I use a split?

There is no risk of damage.  Whether or not sound quality is compromised depends on the output impedance of the DAC, the input impedances of the headphone amplifier and the power amplifier, and possibly also on the lengths and capacitances per unit length of the cables that are involved (especially if either or both of the cables is/are particularly long).  The likelihood of a problem is greatest if the DAC has a tube-based output stage and the two amps are solid state.

A splitter I have used with fine results is this one, made by AudioQuest:

https://www.audioadvisor.com/prodinfo.asp?number=AQM22FHRD

Regards,
-- Al
 

In some rare case (Vincent Audio?) amplifier short its input to ground while power off, an A/B switcher will solve that problem. 

Tell us the model of the dac and it's "output impedance"
And the "input impedance" of the amp (model), and headphone amp (model).
And we’ll work it output.

Cheers George

The DAC is a LAB12 DAC1 SE. I can't find its output impedance but the output level is 2.25Vrms.
I have two amplifiers, Line Magnetic LM34IA with input impedance at 100kΩ and an old Tube Technology Unisis Signature which I can't find any information about input impedance. Then the two headphone amplifiers; Feliks Audio Elise with input impedance at 100kΩ and the other is a Mjölnir KGSSHV but I can't find anything about this units impedance.
Can you come up with something using this ?

While the DAC has a tube-based output stage and therefore might have a relatively high output impedance and consequently drive capability that is somewhat limited, the 100K input impedances you mentioned for one of the integrated amps and one of the headphone amps represent loads that approach being negligible. So I would expect that if the DAC can drive each of the other two units individually with good results, and assuming that none of the interconnect cables would be unusually long and therefore the two sets of cables won’t in combination present the DAC with unusually high capacitance, you are very likely to be ok splitting the signal between the LM34IA and either headphone amp, and between the Tube Technology amp and the Feliks headphone amp. However without knowing the input impedances of the Tube Technology amp and the KGSSHV, as well as the output impedance of the DAC, we can’t predict what would happen with that combination in terms of sonics.

Also, a caveat that occurs to me is that some of the input impedances could conceivably be different when a component is turned off than when it is turned on. So if you proceed with splitters it would be a good idea to verify that when you listen via speakers the sound is the same regardless of whether the headphone amp is on or off, and when you listen via headphones the sound is the same regardless of whether the integrated amp is on or off (with the integrated amp’s volume control turned all the way down, of course).

Regards,
-- Al

While the DAC has a tube-based output stage and therefore might have a relatively high output impedance

For sure, it only has 1 dual triode, half for each channel. If it had two then it’s possible it could have had a white cathode follower output which "can" be quite low, I have a Elekit preamp here which has CF output it and it’s around 100ohms output full range, using a huge coupling cap naturally.

Cheers George