I have found that for CD sound upgrade, I put a Perpetual Technology P3A 24bit D2A converter in line. Improvement was adequate over the Sony internal DAC. Then I upgraded the power supply on the P3A to the optional power supply - WOW - What an improvement!!
The PT P3A is the most inexpensive element in my entire system, but it did the most to improve the sound out of the SCD1!
Worth a try, and they do offer the 30 day return.
(FYI - I am not a dealer and do not have any financial ties to PT - just one heck of a happy customer.)