I'm guessing that you are running SPDIF from the Sonos to the Anthem and using the Anthem's DAC? Also, you don't say if you are making use of any other features of the Anthem for your 2-channel system (e.g., the crossover, EQ, etc.) The answers could affect the advice people give you. Also, maybe you could define what you mean by "lackluster" audio.
In your situation, if I felt the Anthem was the weak link, I would get an external DAC. The Anthem can last you for years of great HT, but DAC technology is evolving so fast that you'll probably want to upgrade/update your DAC more frequently, and it's cheaper to do that than getting a new high-end pre/pro. And it is unlikely that the Anthem's DAC would be competitive with even a moderately priced outboard DAC. Upgrading to the Mcintosh seems unnecessary.
You might also consider either 1) a USB DAC that you can play directly from the computer (bypassing the Sonos), or 2) getting an SPDIF reclocker for the Sonos to feed your DAC. Empirical Audio makes a product called the Pace Car that can be linked to your Sonos (with some modification) to greatly reduce the jitter. I've heard a system with that setup, and it was impressive. You might even consider trying that first, and seeing how the Anthem DAC performs with a reclocked source. If you are still unsatisfied, there are a lot of good DACs out there with SPDIF inputs.
In your situation, if I felt the Anthem was the weak link, I would get an external DAC. The Anthem can last you for years of great HT, but DAC technology is evolving so fast that you'll probably want to upgrade/update your DAC more frequently, and it's cheaper to do that than getting a new high-end pre/pro. And it is unlikely that the Anthem's DAC would be competitive with even a moderately priced outboard DAC. Upgrading to the Mcintosh seems unnecessary.
You might also consider either 1) a USB DAC that you can play directly from the computer (bypassing the Sonos), or 2) getting an SPDIF reclocker for the Sonos to feed your DAC. Empirical Audio makes a product called the Pace Car that can be linked to your Sonos (with some modification) to greatly reduce the jitter. I've heard a system with that setup, and it was impressive. You might even consider trying that first, and seeing how the Anthem DAC performs with a reclocked source. If you are still unsatisfied, there are a lot of good DACs out there with SPDIF inputs.