Yay or Nay

Having used both the Apollo and Cambridge Audio Azur 840C extensively, I can say that the sound between them is rather different.

Big assumption: The DagMagic would be along the lines of the Azur's sound. It is very likely you would see an improvement. However, I agree with Mapman that a tube DAC would further distance you from the Apollo's sound (Likely in a very positive way).

Finally, do not skimp on the Digital cable for the DAC as it has a strong influence on the quality of the resultant sound.

I have used the Monarchy M-24 pre/DAC with several players acting as transports. I used the Rega Saturn with the Monarchy and it was superb, a very rich upgrade in warmth and nice expansion of sound stage from the Saturn alone.

So, I would think that the similar transport of the Apollo would similarly be vastly improved by a good outboard tube DAC.

Oh, forgot; Disclaimer - I reviewed the Saturn, Azur and M-24 for Dagogo.com

Nay.

Adding the Cambridge DAC Magic will be a sideways move at best.

With your present system, you will experience larger benefits by upgrading the
preamp/amp before the source.

However, down the road, adding a better DAC...like a Northstar 192, Paradisea
Havana, or several others higher up the food chain (too many to mention here),
would provide improvement over the stand-alone Rega.

when using the word "improvement", without specifying the nature of improvement is so subjective as to have little utility.

never assume what someone considers as "better". one person's "rupture" is another person's rapture.

it is more useful to be specify expected changes in sound than to use an adjective such as "lateral", "different" or "improvement".

I'm going to say "Nay," only because I know how good the Rega Apollo is as a stand alone player. But I will note that when my Apollo was new I didn't think it was all it was cracked up to be, and in fact, I didn't think it was much of an improvement over my old Rega Planet, which I've long since sold.

It took a good 3 to 4 months of break in before I began to hear the Apollo at its best. At first I used it as a transport for my Monarchy M24 DAC, which I ran directly from its DAC outputs using premium Siemens E88CC gold-pin tubes. But after extended break-in the comparison of the Apollo to the Apollo/M24 combination became a closer contest.

The Apollo stand-alone seemed to have deeper, more articulate bass, perhaps slightly better dynamics, and greater transient speed/clarity. Fast transients like sharp thwacks on a guitar, or sharply plucked strings sounded cleaner and faster.

Then again, on some recordings, the slightly plumper midbass of the M24 was an asset as was its tendency to smooth the music out a bit. The differences were not as huge as many would tend to argue, and my preference for one over the other would hinge on the quality of the recording and the particular instruments contained therein.

I recall getting more dynamic punch and tautness out of the drum kit on a particular Jack Johnson CD, and cleaner, faster guitar work from Tim Reynold's guitar on the solo Apollo. That said, on many vocal recordings and those with brass instruments I preferred the sound of the Apollo/M24 combo. The M24 helped to flesh out brass like the trombone and bass sax.

Ultimately, I ended up selling the M24 and using the Apollo solo. Later, down the road I bought a better tube preamp and although the system sounds just a hair's breadth slower than when using my solid-state passive buffered preamp, I prefer the tube unit's overall presentation. It seems to have a more dimensional soundstage and maintains an excellent sense of dynamic contrasts. It also sounds smoother in the upper-midrange/lower treble area.

If you use other types of source components like a tuner or turntable it may make more sense to upgrade your preamp rather than upgrading to an outboard DAC. This approach worked well for me. Plus you won't need to buy an expensive digital cable and another power cord not to mention finding extra shelf space to accommodate the DAC and possibly a related outboard power supply...