suggestions for updating via DAC.....

IMO the two DACs to beat in the sub $2000 category are Metrum Octave and Teddy Pardo DACs. The first one is more transparent and direct sounding, the other one is more smooth and analog. Do a google search on both.

It would be helpful to know what you are missing with the NAD?
A few years ago I owned the C541i and thought it was great for the $.

An Audio Note 2.1 kit DAC can be had, meticulously built by Pete Fulton, for under 2k, possibly a 3.1

These DACs are non-oversampling, tubed, although limited to 18/96, but imo are extremely hard to beat at their price level. The sound is liquid, relaxed, analog-like, extended, with excellent dynamics and 3-dimensionality.

I recently heard the EE, but have not heard the Metrum. The EE is nice, but does not compare imo to the AN DAC.

I am not in any way business-related to Pete Fulton (digitalpete) but a very happy customer of 2 of his DACs, and have talked to other happy customers of his. Also, I've owned 3 AN DACs and have always come back to them after trying others.

My suggestion.

Buy a Mac Mini, a Wyred4sound DAC 2 (asynchronus USB + pre volume control) and never again fight with disc transport limitations. Probably closer to $2200 but now you can step into 24 bit HD downloads.

"Buy a Mac Mini ... and never again fight with disc transport limitations."

Instead struggles with system configuration, internal CPU noise and the hassles of downloading your CD collection.