Using Sony 300 disk CD changer as transport

How much would a DIP help? There are a few Monarchy on sale but what type of improvement would one expect?

My experience: I had tried a 400 disc Sony 555ES, and even brought it back and tried a second one, only to return that one too.
They sounded like dreck compared to the Sony 9ES 5 disc changer, even the 5 disc 7ES is wayyyy better.
(I own both a 7ES and a 9ES 5 disc changers, and used to have a Sony 89ES 5 disc that played endlessly for 8 years... I mean 12 hours a day, every day!)
Even using an Adcom DAC (which sounds as good decoding the output from the SCD777ES as the CD RCA out from my Sony SCD777ES) The 400 disc changer was total bad bad sound.
Those mega changers spend the money on bells and whistles, and skimp on the basics.
A compromise would be a used Sony 9ES 5 disc changer... good sound and still have a 5 disc changer.

Andy,

I used to run MSB Link DAC II w/ a 70$ dvd player and thought it sounded great, better in some ways than my Cambridge Audio D500SE cd player, which is a well-regarded budget player. I moved on and sold the MSB to a friend who has a much more modest system than mine and who also reported huge improvements when the MSB was inserted into his system. These dacs can be had used for around 150$. They automatically turn themselves on and off when they detect a signal, so your sis wouldn't ever have to fuss with it, and if she doesn't like it or notice an obvious improvement, you could always resell it for what you paid. Worth a try.