Er, depends how it works. If it's modulating the channel directly then yes it'll stay as 8 bit. However, if it's modulating the volume of the channel (I assume it does this) then it'll effectively be 14 bit.
Yes, you're right. The volume knob just multiplies the 8 bit sample by something from 1 to 63 - which would be the same (depending on how exactly the volume works, of course).
Either way, it'd be interesting to compare them.
Sure, maybe someone will code something like that some day.
As I understand it's the maximum output speed from a pair of samples in a buffer, however it's not clear if you can update the samples any faster than the normal maximum playback rate - you might be able to get the CPU to write them but it depends on how faster the buffer updates.
Usually the DAC buffers are updated through DMA and the DMA update rate is limited to two samples per scan line (why this boils down to 28.8 kHz I don't recall, sorry), so you either raise the scan rate or 'manually' feed the buffers from the CPU (just update the buffer before the next sample is played back).
