No the mechanic who told me that its best the keep the injection stock knows what he's talking about. Keep the EFI as stock as possible (of couse a fuel pump upgrade might be needed, and some stuff like that) -- and then add ie 6 more injectors controlled by a piggyback ... that way you can manage everything you need.
If the valves were made of Titanium they would cost a fortune. My guess would be some form of steel alloy, but you just never know when it comes to Japanese metalurgy and engine parts. The Spearco system is proof that you can indeed run a turbo on a 5M with the stock fuel system. 4.5 psi of boost w/o intercooler and 7 psi w/ Spearco liquid intercooler.