The Sony DVP-NS900V modified by TRL is a good option if you can find one. You may also want to call TRL and talk to them about modding your existing CDP, or perhaps let them recommend other CDPs that with mods would fit your budget. I know they have done a number of Sony players, notably the 595 and 777 (see 6moons reviews on these), that would probably get you farther along than any of the options you mentioned.
The DAC is a great suggestion as well. There are several great ones to choose from under $1000 and even at the $500 price point. If your existing CDP is up to being a transport and you splurge on an excellent digital cable this could provide great bang for the buck.