Interesting. I'm new to the idea of using DAC/headphone amps as a pre amp in a 2.1 chan system. What about them will beat the AVR pre amp or your Cambridge Audio stuff? Specs? Audible differences? No doubt a big $ savings at least.
I don't have any measurements for my Cambridge Audio 840E but based on specs, even a $140 headphone amp/preamp can be much better. The ASR bench measurements show that the distortions of a few that have distortions and noise so low that I would think they would be good to match for some of the best measured power amps such as the currently top ranking Benchmark AHB2.
Take a look of the $139.99 Topping L30, for example, and let me know your thoughts:
L30 Desktop Headphone Amplifier-TOPPING (topping-audio.com)
Bench test results:
(3) Topping L30 Headphone Amplifier Review | Audio Science Review (ASR) Forum
Below are the charts that show the ASR (audiosciencereview.com) amplifier ranking by THD+N (reciprocal of SINAD):
You can see that the L30's measured performance well exceed that of the top AHB2, so that's a good thing imo, and you are not going to find any audiophile pre amplifier at any price that would measure better. The drawback of such low cost headphone/preamp is that it has only one analog input, but in terms of pure audio quality, they seem to be practically the best for two channel stereo. For another $200-$500), you should be able to get a DAC that can match (or close enough) this preamp's bench test performance.
Power amps ranking chart based on SINAD at 5 W output:
