So the company that you asked gave you the correct answer.

If you want best finish,what you miss to understand here is what material and price. There are blocks or thick sheets of some compounds that could have perfect finish but they are not cheap. The wood will always need sanding from 60 grit if you use cheap pine. MDB will be ok, but then you need to treat it additionally.

So to resume what i believe is the correct answer:
1. IMO you need custom sturdy cnc with high Z axis/200mm or more/ and fitted with extra 3D printer head. 1kg of material is cheap 15eu or a bit more and you put it where you need it, no waste here and there. Then you machine it where and when necessary. Note should be taken that it will never be perfect perfect, you will need to sand and possibly flame polish for industrial look.
The bad thing is that it could never be a production, just a way to make cheap prototype. The 3d print i mean. And it will take you a lot of time to learn both.

2. for starters- cnc + what you are doing till now . Instead just implement 3d paths so the curves are smooth. Or do it 2 pieces. Of course if you go with 2 or more pieces split, you will need jigs about each step of the process.


One thing you should understand though. What you aim to do will always be done better if you make one piece, perfect it as much as possible and then cast it from whatever resin. If you can not, then hire somebody to teach you and make you the mold. That will be cheapest and fastest.

Of course that depends on what people would pay money for, if the idea is to be done artistically and finished by hand or they would care only for the custom acoustics.