Benefit of a DAC for a good red book cd player

I'm with your friends. Don't bother. Enjoy your Apollo! IIRC that was a well-respected unit, so it may be hard to do better without spending a lot on a DAC. Two big issues are jitter (in the Rega as a transport, and in the ability of the new DAC to reject jitter), and your hopes/expectations for change. What is it that you are hoping to gain?

I'd look for someone who has done this with the Rega Apollo, rather than accepting generalized forum feedback based on other CD transports.

The best DAC's will present the music more holistically and naturally, without any harshness or glare. IMHO, it would be worth investing in a really good DAC that you could use in the future as you evolve towards other storage media, such as using HD-downloads at higher bit-rates than CD.

That is a whole lot more future-proof than investing in a dead format, like CD's are becoming. Of course, I speak with forked tongue, since I continue to invest in LP's...

If you are willing to look at the higher-priced DAC's then I'm sure you'll find some that will be a big advancement over the internal one in the Apollo. Otherwise, you'll spend money for perhaps a different sound, but doubtfully a better one.

Hope this helps!