But what defines a professional interface?
Having Pro in the name?
If a pro uses a soundblaster then surely it becomes a pro interface?
Personally I'd say there's a lot more to worry about before even thinking about converters, to name a few:
Room accoustics for both mixing and recording;
good, well arranged material, well rehersed and ready to go;
good instruments and performers to play and sing the material;
mic choice and positioning for good capture;
The right preamps chosen based on desired coloration, clarity or anything in between;
correct gain staging;
monitors that can acurately reproduce the recorded sound in an ideal listening environment;
and so on.
Once all of that is perfect and in place I might think about if there is a need to worry about the effect miniscule conversion errors/distortion could have on my recording.
and of course there is always the consideration that some of the more desired gear out there is so lusted after because of it's actual lack of perfect fidelity and the distortion it introduces although I doubt anyone is sitting with dreamy eyes reminiscing about "that soundblaster sound"
I have a long way to go yet