On board or outboard DAC?

gdnrbob,
I appreciate the response. The more I dig into this the more I feel that I may be best off to leave well enough alone. We always look for that one more tweak to make our systems better. I think I'll just stick with what I have.

Falconquest, I also have the Ayre C5XEmp and have tried my Rega DAC and was about 10 seconds into a song and realized I was not going to do that. The I bought a Oppo 105d for use as a BluRay and 5.1 music. I have tried playing Redbook and 2Channel SACD and again, return to the Ayre. I realize the Simaudio is better than the Rega, but my thoughts are that the Ayre is very tough to beat. I would think a very expensive DAC would probably show improvement but then a risk of jitter may come into play as a new issue.

just my opinions 

seems easy enough to try and compare, both your Ayre and Simaudio are outstanding products...

I believe the interfaces are compatible, so all you need is a balanced to single-ended converter on the Ayre and a digital coax cable in order to send data to the Simaudio DAC. That being said, I also own a C-5xeMP and I haven't heard a DAC best it in terms of sound quality. If I ever listen to Ayre's new QX-5 Twenty, I may sing a different tune.

Just from the perspective of flexibility and adaptability I would opt for the outboard DAC.

That way I can...
- use the IC's I believe provide the best sonic performance
- use the best Power cables  I believe is best suited to the component
- change to another DAC as the technology improves

Inboard DACs may be constrained by "design decisions" that are based more on implementation costs than sonic performance - even in some high end gear unfortunately.
- Also, having the DAC share the power supply with a power hungry amp stage  may not be the best solution, sonically or operationally

Regards...