Have a look here: https://hifiduino.wordpress.com/intr...-to-hifiduino/
It is not exactly what you want to achieve but it gives you a very good idea how arduino can be used in HiFi equipment.
I imagine you will need some input interface as well. A rotary encoder, push buttons? And some sort display - well maybe not - you might be able to attach an LED in parallel to each relay.

Here's mine:IMG_0870.jpgIMG_0869.jpg

ULN2003 looks pretty cool. It will solve lots of issues for you!