I talked to a friend of mine who builds high performance engines and posed the "acoustically tuned" airbox question to him. Well, he looked at me like I was crazy and said, "I doubt that you will have any issues there as the new '08 vettes are just getting acoustically tuned manifolds and the crossfire's engine is a much older design."

So I decided to finally use my B.S. degree and examine the equations the motorcycle guy had up on his page...

According to him (or her?), for our engines (V6):
Resonant RPM = 28650 sqrt (116.5 A / VL)

But in our case, since we have dual snorkels that are 70mm and round, cross sectional areas are doubled.

V = (Left intake area + Right intake area) L

V = 2 * A * L

Simplifying we get:
Resonant RPM = 28650 sqrt (116.5 A / (2AL) L)

Resonant RPM = 28650 sqrt (116.5 / 2LL)

Resonant RPM = 28650 sqrt (58.25 / LL)

Resonant RPM = 28650 sqrt (58.25) / L

Resonant RPM = 218661 / Length

Or in our case:

Intake Length = 218661 / RPM

if we solve for an RPM less than or equal to our red line... We can see for our airbox to be "acoustically tuned" to our engines (6,000 RPM or less), the intake plenum length would have to be over 36 meters (or 118 feet) long!