My take:
the MARANTZ AVR is the weak point and known compromise in your HT system performance for maximizing your 2-channel audio music enjoyment.
Both @soix and @gkelly both have a valid point IMO. The preamp in any AVR is primarily focused on HT with its artificial multichannel glitzy features at the distinct and not insignificant compromise for 2-channel audio performance maximization.
At what pricepoint of external DAC are you considering to add in ? Inserting an external quality build DAC representative of the same build and price-point strata of the rest of your system, but still using the direct outs pathway from the AVR preamp, won’t provide you a meaningful 2-channel audio performance step-up you seek. ( if any ).
Similarly, in the context of $$ paid versus value received, I am highly skeptical that a more modest budget class external DAC won’t provide that “aha!” or “Jesus moment “ stepup from what you have in the AVR now.
Budgets matter big-time for sure…we all face that $$ compromise in our journey down the Yellow Brick Road to the Emerald City in Audio OZ. Until you can comfortably consider a proper upstream reworking of your HT audio system for added performance emphasis for 2-channel audio , I would live with what you have now.
This crazy hobby maximization is a journey and not a quick shortcut destination.
Good luck, sir , and choose wisely.
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