AD TxDAC - quadrature digital modulation purpose ?

Hi!

While learning about QAM modulation (in context of DVB-C transmission)
I came to Analog Devices AD9773 TxDAC datasheet. I'm slighlty confused
with its digital complex modulator. Could someone read below and check
my understanding ?

If I understand correctly, one mode of operation is to output plain I/Q
signals and mix them using external analog quadrature modulator (e.g.
AD8345). In this mode complex baseband signal (which has "DC-centered"
spectrum) is simply shifted to a carrier frequency.
If complex baseband signal has a frequncy range berween -B and B, as a
result of modulation one gets a real signal with frequency range [Fc-B,
Fc+B]. Right ?

Another mode is the one that employs digital complex modulator
(operating at fraction of sampling rate) and analog quadrature
modulator, as above. It is said in the datasheet that this allow image
rejection. I'm not sure if I understand what image is the talk about,
and thus what's the advantage of this additional modulation.

My (possibly wrong) understanding is that the images of the baseband
spectrum needs to be removed only if we do 2 stage upconversion, with
low IF carrier quadrature-modulated by the baseband signal to a _real_
IF signal, and standard heterodyne upconversion. Does it make any sense
?

BR,
Przemyslaw