as Christian says.
From my few months with a CD5, I recall a smooth sound, with maybe slightly recessed detail (mind you, I was comparing with a CD3.5 and a CDX...).
For the CD5, I found the following changes delivered good improvements, without modding -
AR Sound Green Link din-din signal cable (more detail, more bass definition)
Avondale SPX psu - In my experience this is pound-for-pound the best psu for mid-range Naim CD players. At one stage I had a HiCap, SPX and Sonic Bliss available for direct comparison, and the SPX was (for me) the most musical and engaging.
Power Cable - I have found that a decent after-market screened cable raises the game of Naim CD players and Amps. As Christian says, it need not cost the earth to find out. Speaking of earth, opting for a hydra may bring add some clarity to proceedings.
Lastly, Naim CD players do respond to isolation platforms, and need to be absolutely flat. So there's a definite need for a spirit level, plus room to experiment with the best platform material to your ears - glass / wood / MDF / marble / Granite etc