Try using the W4S as a DAC only, and use the pre-amp section of the NAD, just to see what happens.
The symptoms you are describing are usually early in the chain and I've owned the W4S and NAD, and neither are harsh.
If you are looking to upgrade, stop using the W4S as a pre-amp, it's a good DAC but not a good pre-amp. I'd be looking for a much better integrated amp in the short term, along with a review of your USB cable and interconnects (dac to integrated). They will have the biggest impact at resolving your issues.
The symptoms you are describing are usually early in the chain and I've owned the W4S and NAD, and neither are harsh.
If you are looking to upgrade, stop using the W4S as a pre-amp, it's a good DAC but not a good pre-amp. I'd be looking for a much better integrated amp in the short term, along with a review of your USB cable and interconnects (dac to integrated). They will have the biggest impact at resolving your issues.