All Digital Audio G4s accept dual processor upgrades.
However there is no such thing as a Digital Audio 400MHz. That would be the Sawtooth, or Gigabit Ethernet. Some earlier versions of those do not accept dualies. You need to check with the vendor.
Digital Audio originally shipped in 466, 533, 667 and 733; later in higher speeds.
OWC is good; as for the processor upgrade you might want to also check on something like a Sonnet 1.2GHz single.
NO, you need to check the revision number of your Uni-N (Northbridge) chip on the motherboard to see if IT supports dual processors. On OWC's tech support page, there is a free checker utility you can download & use to find out
NO, you need to check the revision number of your Uni-N (Northbridge) chip on the motherboard to see if IT supports dual processors. On OWC's tech support page, there is a free checker utility you can download & use to find out
Which is part of what makes OWC a good vendor. Let's be fair here -- most folk haven't heard of Uni-N and would probably want to ask the vendor, and I myself do not know which revisions of the chip would not accept dualies; it's handy when a vendor provides you with the tools to help yourself but not typical.