I have the exact same issue. Seperate microphone track and the audio from the main track works without a problem. However the microphone track is always super stuttery. I actually disabled all C-State (or in the case for my motherboard it was the options C1E, C3 and C6/7) options I could find in my bios settings. However the stutter in the microphone track (or the main audio track if no seperate track is used) persists. So that sadly did not fix it for me. :/
I would love to use ReLife, but the audio issue will mean I will stay with Dxtory for the time being. I hope this will get fixed soon.
This isn't the first topic I see about this issue.
Should it help I am using an Asus Xonar DS Sound card and use a Sapphire RX 580 8GB Nitro+.
I also noticed that when I am using the microphone input (NOT the record microphone option, but rather using the microphone input as the Audio Capture Device) as the main and only audio input ReLive still records ingame sound for some reason. Microphone only gets recorded when I am actually using the record microphone function and in that case the audio stutters as mentioned above.