Will a new Dac improve the sound?

I have a Cary 303, which I believe is older and more expensive than the cdp1. I use it as a transport for a bricasti m3. The m3 is a giant reduction in distortion from the 303 dac. Smoother and more detailed, a huge improvement. as a transport the 303 is better than my iMac through the Ethernet input. 

In decades past I used transports with outboard DACs. Being retired for 5+ years living on SS, I streamlined my front end , making due using my Oppo 105 (with aftermarket power supply). The following worked out for me because I have an Audio Alchemy DDP-1 + PS 5, a dac/pre. So, then I used an old Pioneer PD65 with level 3 Musical Concept mod as a transport (but it only had toslink out) for redbook, and used that until it died. I replaced it with a Marantz HD CD-1 player, used as a transport but with coax out, but like the PD65, the laser mechanism died, parts are no longer available, BUT, I could buy a laser assembly for $150 + shipping from Asia. However, I came across a fantastic review of the Audiolab CDT 6000, and found a slightly used one on AG at a price I could afford. The level of improved musical enjoyment jumped quantum levels, still surprising me months after the purchase. From my experience, unless you have an exotic ($$$$$) player, it likely has an average laser mechanism and circuit

hth

Yes it will. I made tests with different CD players. A separate DAC, even a modest one,  will give you a notable difference. If the DAC in your CD player is not really good and you choose a good DAC, the improvement will be very essential.