How to get HIGHEST settings on NVR

Hi,

I have a DS-7608NI-K2/8p

Currently, if I set my 8MP cameras to Highest image quality they do not record or run on live view at any frame rate.

I lower that to the 'Higher' setting then they run even at 20 FPS.

Is there something I should be doing differently?

I'm slowly replacing all my cameras. Eventually I will have 6x 8MP.

What is currently the best NVR for this? Or is it not an NVR issue?

Thanks