YOU DON"T NEED A BETTER CONVERTER!....
You would be shocked if I told you how many major label artists and producers are tracking their beats with 002 converters! They are actually not bad at all... I sold my HD ACcel system and got a 002 for the house and I bet you if I played the same kick tracked through the 192 and the 002 you wouldn't be able to tell the difference. We are talking about tracking synths, keyboards and MPC's, which are dynamically loud sound sources to begin with. You won't notice the huge sonic improvement on these kinds of sources. Especially if you have a compressor in front of the converter and are getting a nice hot level into it.
How are you tracking your MPC into the 002??? Let me guess... You've got your keyboard plugged directly into the back of the 002, right? There's your problem... The MPC put's out an unbalanced high impedance "instrument level"... What you ideally would want is for the 002 to see a balanced +4 "line level". This is what a DI is for. Most high quality preamps come with really good DI's, like the GTQ which we talked about in another thread. It doesn't matter what kind of converter you are using... if you don't have a good DI/ preamp it will always sound weak.
You need to get a good preamp/ DI to track through. It's as simple as that. Or you could blow your money on a converter and keep having the same problem that you have now.
Also, the U5 is not good for "signal warming", it is actually quite good for the opposite though. I would use it if I wanted a semi-bright crisp sound.... If you want a "warm sound" or round bottom end, then the best way to go is a Neve style preamp.