Not sure what to make of the specs- based on those specs of theirs, the 68c has higher Mic In THD+N compared to that of even the 24c, which in this Youtube review was measured to have significantly high distortion
PreSonus Studio 24c Audio Interface Review (audio quality test) - YouTube
As an owner of the M2 I'd be biased and say go for the M2 and sleep well knowing that you've made a solid purchase consistently backed by third party measurements from different sites
Presonus fluctuates a lot on their audio interfaces in the same lineup, i saw this simple video of specs compared in a non scientific way between 24c VS 26c VS 68c VS 1810c :
(take a look)
For example 24c is quite bad on some specifications compared to other models while 68c is the almost the same as 1810c.
For 24c
ADC : 108 dB
DAC : 108 dB
Microphone Inputs
Gain Range: 50 dB
Dynamic Range: 106 dB (A-wtd, min gain)
THD + N 0.004% (1 kHz, -1 dBFS, min gain)
EIN-126 dBu (A-weighted, 150Ω, max gain)
Instrument Inputs
Gain Range 50 dB
Dynamic Range 105 dB (A-wtd, unity gain)
THD + N 0.002% (1 kHz, min gain)
Headphone Outputs
Maximum Power 47 mW / channel @ 56Ω
Dynamic Range 83 dB (A-wtd, 56Ω load)
THD + N 0.01% (1 kHz, 0 dBFS, loaded)
Impedance Working Range 32Ω to 300Ω
For 26c
ADC : 114 dB
DAC : 114 dB
Microphone Inputs
Gain Range: 70 dB
Dynamic Range: 110 dB (A-wtd, min gain)
THD + N 0.004% (1 kHz, -1 dBFS, unity gain)
EIN-125 dBu (max gain, 150Ω, A-wtd)
Instrument Inputs
Gain Range 70 dB
Dynamic Range 110 dB (A-wtd, unity gain)
THD + N 0.007% (1 kHz, -1 dBFS, min gain)
Headphone Outputs
Maximum Power 30 mW/channel (56Ω load)
Dynamic Range 104 dB (A-wtd, 56Ω load)
THD + N0.009% (1 kHz, -1 dBFS, no load)
Impedance Working Range 32Ω to 300Ω
For 68c
ADC : 114 dB
DAC : 114 dB
Microphone Inputs
Gain Range: 80 dB
Dynamic Range: 114 dB (A-wtd, min gain)
THD + N 0.007% (1 kHz, -1 dBFS, min gain)
EIN-130 dBu (max gain, 150Ω, A-wtd)
Instrument Inputs
Gain Range 70 dB
Dynamic Range 110 dB (A-wtd, unity gain)
THD + N 0.007% (1 kHz, -1 dBFS, min gain)
Headphone Outputs
Maximum Power 150 mW/channel (56Ω load)
Dynamic Range 107 dB (A-wtd, 56Ω load)
THD + N 0.002% (1 kHz, -1 dBFS, no load)
What will happen when the 3000-5000 hour capacitors die like in the article below ? :
https://www.audiosciencereview.com/...analysis-and-few-in-house-measurements.17819/
If you keep the device on, the capacitors work all the time. It will die after that ?