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.
Kinda surprised the transport is still working. Those were notoriuos for failing.
How about isolation device(s), power cord & cable upgrade, shunyata stone?
I own a DCD 1500mk2 and a DCD1420 Denon cd players. I am considering buying a dac for them.That is one possible upgrade you might want to look into.Also, you might want to upgrade to a DCD1650AR,there is one for sale here on Audiogon.