jnejman,
Yes, 8 cylinders will inherently produce a deeper sound. However, the characteristics of the sound and rhythm all depend on the firing order of the engine. For instance, 5.0 Mustangs have a very characteristic sound that is different from a Chevy V-8. The difference is not in the mufflers - I have the same mufflers on my Camaro as my buddy does on his '94 Cobra. His car has the very distinctive "Mustang sound." My car sounds completely different even though it has the same mufflers because it has a very different firing order - this sets up different harmonics and pressures in the exhaust system. Both cars have a deep, throaty sound, but the firing order on a Ford V8 produces a smooth, monotone kind of sound that some describe as a "drone." The Chevy V8s have a more rhythmic, more interesting oscillating exhaust note that changes tone throughout the engine's revolution This is directly due to the way the firing order criss-crosses across the block.
My point is, it will be a deeper note, but the actual sound characteristics have a lot to do with the way the engine fires.