I'm looking for a shop with a good selection of earphones like Sennheiser or other brands wich is better than the usual 60 pesos quality earphones you can find at every corner. Any recommendations?
I have no idea what kind of earphones you're looking for, but if they are bigger than buds, you could try the music supply area.
Talcahuano from Corrientes to ~Peron (or Mitre) and then up Sarmiento and Peron towards Callao. Especially Sarmiento. They have music instruments galore and probably have higher end headphones like this:
I have no idea what you're really looking for though. I do know that Macstation should be nice and expensive.