I honestly don’t know. I use the built-in soundcard on my Mk3 and it sounds fine to me.
The built-in effects in Maschine are decent and usable, but also economical in terms of CPU usage. Luckily, it’s a fine plug-in host, so you can just add a high-end reverb or more interesting sounding delay easily. (Make sure to look into the aux routing options for how to set up send effects when you start doing this to keep CPU usage sane!)
The sampler sounds great to me, and the new real-time time stretching in the built-in audio plugin is surprisingly high quality imho.
I agree that the filter in the built-in sampler is not special, but I don’t think it is intended a such. Just add a plugin after it if you’re after a specific filter character instead of more transparant control.