Elektron Musical Instruments

My SidStation is, as I'm sure anyone who owns one will know, an 
excellent source of dirty and wild sounds. I use it more as a noise 
generator than a synthesiser per se.

But the only thing that really annoys me about its sound is the 
constant hiss. Whether you're playing it or just letting it rumble 
along, there is almost always a tape hiss transmitted with the sound. 
Occasionally I manage to get rid of it with cunning use of the 
low/bandpass filter but usually that also removes the higher 
qualities from a sound I wanted to preserve! So I EQ it using 
SoundForge's more complicated filter, to try and salvage as much of 
the SidStation's sound as I can whilst still cleaning away the hiss.

Does anyone know if the hiss is inherent to 8-bit synthesis?

What about replacing the SidStation's phono output with a SP/DIF one? 
I'm no technician but if it were possible to get that modification 
done, would it improve the sound quality?