Upgrades/tweaks for classic Denon DCD-1500??

Hi techies: Anyone out there know if there are DAC upgrades for the vintage Denon DCD-1500 CD player. I've had mine for about 20 years, and those of you familiar with it know of it's rock-solid 20+ pound structure and unerring transport. Extremely silent operation and great stereo separation. I'm sure the DAC's are long in the tooth, though, and I'm sure I'm missing out on some sound quality. Any tweaks available? Thanks.