Is a femto clock important if you aren't using asynch USB?

My guess is that the OP is correct, that since usb is the most jitter prone interface, the lack of the femto clock isn’t so important. I remember looking at the W4S DAC a few years back and they were offering the non Femto for about $1900 and the Femto for about $2600. Later I learned that the price of the Femto chip to the manufacturer was $10.

As to @lordmelton point, the DAC in the Node2i is a significant improvement over its previous DAC. The OP may not actually get much of an improvement using the older W4S DAC. If the W4S is going for a low price it might be worth it, but not if the seller wants more than $500 or thereabouts

Topping D90 ($900) is a better choice than the W4S.

While it is true that USB does not rely upon the streamers clock, it seems to me that you want a good DAC clock for stable sampling of any input.

Seems?

What you really should want is a modern DAC instead of worrying about clocks.

I like buying used but never do it with Digital gear.    I did buy a R2R DAC ,  but I also have a DAC that can do DSD.     When I bought my streamer I wanted the latest tech and codecs.     I am a late adopter when it comes to everything else.....