It took a bit for me to understand what I was looking at, but it's 4 AFEs with a set of anti-alias filters leading to the ADCs. LeCroy uses the same filter for 2 GS/S as for 4 GS/S. So in 4 channel mode all your data are aliased. Caveat emptor.
However, the physical topology is such that it is very simple to run SMA cables to and from SP6T relays placed where the CRT used to be. A $90 or less VGA monitor takes care of the display. The VGA/parallel port card has an internal VGA output. So with a RPi 10" monitor and a short VGA cable replacing the CRT is about as easy as it gets.
This would allow collecting good data for:
four 750 MHz channels
two 1.5 GHz channel
one 3 GHz channel
true ETS/RIS sampling
The Fc values reflect a -3dB point consistent with minimal (<1 %) overshoot.
Does anyone else have a DDA-120/125? At realistic eBay prices, they are very cheap for what you can get with some modifications.