I may have solved the EDUX ADC buffer amplifier topology riddle.
As we know, EDUX has an additional amplifier stage (Intersil EL5166) in front of the ADC differential buffer amplifier. Looking at the resistor values, voltage gain can be calculated for each scope model and each gain stage. The following simplified schematic shows the topology and gain figures for each scope model. It can be seen the overall gain for each scope model is the same, Av=8.46.
So why in EDUX model the second stage has gain of only 2 , whereas in DSOX it is 8.46 ? Well, I am glad you asked. Assuming the second gain stage IC in EDUX is LMH6550 (vs LMH6552 in DSOX 1000X), which is a 90MHz bandwidth amplifier, we check the datasheet (we are not rigol employees, so we always check datasheets) and find a gain/bandwidth chart that shows most of the bandwidth is utilized with Gain=2.
Now, in order to maintain the ADC input level, we need to boost the signal to the same level as in DSOX. Additional gain that is required for that is 8.46/2=4.23. So there has to be a pre-amp and that is what the EL5166 must be doing in EDUX. Looking at its voltage gain figure - you guessed it - it is 4.23.
So the combilned gain in the dual stage EDUX buffer amplifier is exactly the same as in DSOX single stage one. The DSOX just achieves it with a single LMH6552 wideband amplifier. In EDUX the lower bandwidth amplifier ICs are used to help limit the bandwidth. Looking at the EL5166 datasheet (we are not rigol employees, we always check datasheets) it can be seen the bandwidth pretty much mirrors LMH6552 bandwidth when the latter is set to gain=2. Both start rolling off after 50MHz.
So there you go. The buffer amplifier in EDUX is a limited bandwidth component and certainly has to be replaced with that of DSOX as user TK has done in order to extend the front end bandwidth in addition to straping and software options. Also, the bandpass filter at the output of the buffer amplifier must be measured and adjusted as required to support the extended front end bandwidth.
Weird - comparing Digikey pricing, looks like they're spending more on the 50MHz front-end than the 200MHz one!
A quick pricing check at Digikey showed that price of EDUX's 2-stage EL5166+LMH6550 and DSOX single LMH6552 is pretty much the same. So no, does not seem they are spending more on the EDUX front-end.