Humm...I was just going by what 949 Racing has for the Tomei cams:
"* The NA8 BP05 cams will work with OEM lifters, valve springs and ECU provided either OEM intake or exhaust is used.
* If high flow intake and exhaust are both used with any of the cams on this page, the OEM ECU will not provide enough fuel potentially leading a a dangerously lean condition (boom!). Additional power gains will be found with a fully programmable ECU regardless of what other parts are fitted to the engine."
http://949racing.com/Tomei-miata-cam.aspx
Obviously these are B6 HKS cams so maybe they are more aggressive and the B6 ecu isn't as capable as the BP...