Yes; kinda, maybe, sort of. Being a electrical design engineer, I design a log of amplifiers and analog control electronics at work. So naturally, I do this at home with some of my equipment. For a while, I was doing custom electronic design for folks who had high end stereos.
The key is finding where the weak spots are in the equipment, then making those spots more robust. By weak spots, I mean where the designer left performance on the table and didn't pack it into the product. Anyone can tweak stuff, which may or may not sound better, and may not give you much bang for your buck. And, trust me, hiring someone to do custom engineering on your equipment is expensive.
If you go this route, pick someone who routinely modifies your brand and model often. That is, they have a long history of fixing that particular model. Ideally, they should be someone who actually worked at the factory or someone who worked in their service dept. If they don't meet this criteria, don't send them your equipment or money!
The key is finding where the weak spots are in the equipment, then making those spots more robust. By weak spots, I mean where the designer left performance on the table and didn't pack it into the product. Anyone can tweak stuff, which may or may not sound better, and may not give you much bang for your buck. And, trust me, hiring someone to do custom engineering on your equipment is expensive.
If you go this route, pick someone who routinely modifies your brand and model often. That is, they have a long history of fixing that particular model. Ideally, they should be someone who actually worked at the factory or someone who worked in their service dept. If they don't meet this criteria, don't send them your equipment or money!