All,
To go into my Axiom HT setup, I plan to purchase another Sonos zone (unit) when the wallet allows. I have a had a couple of recommendations to also use an external DAC. Is this worth it? What's the rationale for using an external DAC vs. just feeding an optical cable into my Pioneer SC-05? I have zero experience in this area so would appreciate your input.

Some people prefer the ultra high end stand alone DACs, to those built into a receiver. In practice there's little difference once you get into the higher end receivers, which the Pioneer Elite definitely qualify.

Now that multi-channel, HD audio is being fed over HDMI, it becomes much more difficult to make use of S/PDIF DACs anyway.

Although, I do plan to get a Benchmark DAC1 someday to feed the stereo monitors in my small bedroom studio.

Dan, as far as the digital to analog conversion itself goes, DAC chips have been a mature technology for quite a few years now. The small measurable differences that still exist aren't audibly significant and even those used in modest cost receivers perform the conversion function without audible flaws. As in almost everything in audio(even pieces of wire)we read reports using flowery language to describe the benefits of the new DAC, but unless some electronic circuit was included which degrades the sonic accuracy, there's no factual support for any different results. Save your money for something which can make an actual improvement.

Thanks Chris and JohnK,
You just confirmed why I was questioning the advice in the 1st place. The money will be saved for better things.

It being a mature technology has not stopped many devices from being junk. The amount of 5532/4s being used in hi-fi gear is proof of this.

I bought an MCM electronics 50-7774, replaced the junk 4558 output stage with a LME49722MA, the wall wart power supply with a power one linear 12vdc one, the output & coupling caps with film ones. It cost under $110 and it is better than any high priced receiver I've used.

It's a mature technology but all the cost cutting measures that go into making receivers don't make it difficult for my $79 box with a few changes to be a better stereo DAC than what's in a $3K receiver or many $600-$800 pieces.

There is a saying, digital smart, analog stupid about all the amazing things modern electronics can do, while still missing the analog basics that can make a big difference. A look inside many modern devices proves this true.

Even with something like the MCM 50-7774, you end up going into the line-ins of a receiver, through its analog signal path (if it has one, and doesn't just digitize everything from the start), then through its pre-amp, and finally its output into the power amp. Additionally, if the analog ins don't pass through an ADC, you won't get any sort of bass management.

I don't see any advantage of pairing a DAC with a receiver.

Now, if the DAC provides a high quality pre-amp (or you have an external) for volume control, and it connected directly to a power amp, driving full-range speakers without a sub. Then, there may be a reason to go with a DAC.