Ciao Andrea…
For round corner i use a homemade router table (toupie), on foto you can see the tool for round corner. My DIY toupie is very useful…
For the other question, I never bought kit or other. Make our circuits and PCB is a part of the fun… 
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I reuse sometime switching PSU for NO AUDIO SERVICE (only for led, remote receiver or relays). In my preamp (BOZ) you can see in right corner PSU for LED. RIAA preamp (left wall in photo), Relays board with encoder, Mosfet preamp are homemade.
In my CD Player all PCB are homemade: DAC, CD IDE interface, DAC supply and antibump…
Even remote are homemade, I have a lot o fun to build them…
That’s all 
