If we don't have measurements for the MR4's heapdhones output or your motherboard's output, we can't really say.
However, even if they are just average, they are likely good enough.
If you don't hear any hiss and can get loud enough, you're good.
Feel free to buy a well measuring device, of course, but one that gives you better usability or extra features compared to what you already have.
On-board EQ, virtual surround effects, a nice volume knob, microphone input are examples of such features.
During my experience with onboard audio (and cheaper devices in general), I've seen following issues:
1. Most important - system-wide audio effects that are not easily disabled.
This ranges from a mild EQ to very spacy "3d" effects and heavy-handed dynamic compression.
You can easily test for this by playing back a file in Foobar2000 (or any audio player with WASAPI Exclusive output). During playback, switch from default sound output to WASAPI Exclusive and if you hear an obvious difference, then there is something enabled.
If you don't like those effects and disabling them is impossible or just too cumbersome, it's a good idea to get even a simple dongle DAC.
2. Noise
If you hear any hiss or other noise and it disturbs you, get another source.
If not, you're not going to get better sound if you get a new source with less noise.
3. High output impedance
This can change tonal balance.
If you have access to your headphones' impedance curve, a higher output impedance will amplify the frequencies where the headphones' impedance is higher than the "average".
This can particularly upset the tonality of multi-driver IEMs, but sometimes people want this effect (a classic example is Sennheiser HD 650 with a tube amp).
With FT1 Pro the impedance curve is flat (as with most planars, I believe), so you're not going to get a change in the tonal balance.
You will, however, lose power output - maximum volume will be reduced. Quite a lot with OTL Tube amps. Not so much with your average onboard audio, at least in my experience.
