Magfan - I forgot to answer aliasing. In sampling theory, input signal frequencies that exceed the Nyquist frequency are "aliased." That is, they are "folded back" or replicated at other positions in the spectrum above and below the Nyquist frequency. In case of DAC it is easy to see what happens when you make drawing of a few cycles of sine-wave on the paper. Now imagine that you the frequency of the output samples is less than 2x signal frequency (period longer than 1/2 of the signal period). Lets take period of 3/4. Placing first point at zero we'll get second point at 3/4 (-1) next at next 3/4 (0) then +1 etc. When you connect all the points you will get sine-wave with +/-1 amplitude and frequency of 0.33 of the original signal frequency.
Let take signal of 33kHz and DAC update frequency of 44kHz (1.33x). In result DAC will output (instead of 33kHz) 11kHz (0.33x) at full amplitude (33kHz - 44kHz/2). Nyquist says that in order to preserve frequency information we have to either output them at >2x their frequency or to not have them at all (filter them out) otherwise they will fold starting from 0Hz (DAC will output 22.05kHz as 0Hz and 22.1kHz as 50 Hz, 22.2kHz as 150Hz etc.