Shielded cable is preferred, but unshielded cable is apparently acceptable when routed properly. If you want to provide the best product possible, but for an affordable price, you need to spend your budget on the right parts. Money spent on cable can not be used for caps or transformers.
Personally, I like this no-nonsense philosophy: if it works, why not? There's probably lots of gear around that isn't worth its money because its creators had other priorities than sound-value for money ;)
Regards,
Hans