[hetman]

You're right in that only the libiio firmware relies on the CPU to forward the samples out to the ethernet interface. The UHD firmware on the other hand does not seem to occupy the CPU to do this, however I have still had trouble getting transfer speeds to go much faster than they do with libiio (and I've had a lot of other problems with UHD personally). I'm not certain what could cause this limitation though.

In theory the hardware probably could do what you're describing if someone wanted to hack the FPGA internals themselves. I'd love to hear if you ever have any success getting things running better.