PELL, thanks for taking and sharing these photos.
Basically, here we've got the usual layout of an AWG with the SOC module, FPGA with attached smaple memory, high-speed DAC (here 2.5GSa/s), PLL section (labeled "unknown"), switched attenuators (relays close to the outputs) and some high speed output amplifiers / drivers.
I find two details quite interesting here: Rigol provided two different reconstruction filters for each channel that are assiged to the (individually switchable) four outputs of the Texas Instruments DAC38J82. This may be related to the two product lines (DG800 Pro and DG900 Pro) with their considerably different sample frequencies to be able to get along with a single hardware, but it may also provide for different filter envelopes for certain frequency ranges or waveform shapes (I rather assume it's the first...
). The other peculiar detail is that Rigol spun their own output driver hybrid. It appears to be a metal core PCB with either bonded or soldered amplifiers and passives that have afterwards been potted in epoxy. Since the AWG doesn't provide any higher output amplitude than "conventional" approaches with TI's THS3491 (or its siblings), and the output drivers of an AWG are at least somewhat exposed to "mishaps", I consider the utilization of a hybrid module here rather disadvantageous -- a DIY repair would hardly be possible and I doubt Rigol would provide these hybrids to customers as spares.
Shame that Rigol didn't attach the DAC with all eight high-speed serial lanes to the FPGA (maybe the FPGA doesn't provide more connectivity,
I didn't check for that just consulted the DS: the Artix in the 15x15mm² enclosure is only available with a maximum of 4 GTP transceivers, so in order to use all 8 lanes, a higher FPGA type would have been req'd); otherwise it should have been possible to run the hardware at the DAC's full 2.5MSa/s.
Otherwise, I'ld bet that the 800 Pro can be made believe it's a 900 Pro -- which it actually probably is anyway, except for some calibration points, just like the "non-Pro" versions were.