Modded Players

Honestly would suggest doing a search as there are many options. Yes, they can produce extraordinary results.

Actaully I think that the mod price on the Sony 900 through TRL may be getting raised to $750 due the extensive labor involved, but they could tell you if they have implemented that new price yet.

Other places to research are Modwright and Empirical Audio.

TRL has done 600+ players in the past year and has done about anything you can think of including very very high priced units.
Like most modders, they can improve any unit. Like most modders they have their favorites.
They have had the best results with the Marantz SA14 and the Sony dvp ns900. Both units are out of production but can be found used. The Marantz for around $1100 and the Sony for $3-400. I have had both in my system. Very nice.
The price of the mod is $550 on the Marantz and I think $750 on the Sony now.
Modwright does some work on SOnys adding a tube stage that is very well liked by many people.

Look around-you don't have to spend a fortune to get great sound. Also digital is the worst investment in audio so spending several thousand dollars is not only not necessary-it is crazy unless you have to have a certain model for some reason.