As mentioned earlier, your requirements make this rather a difficult system to configure.... largely dominated by the problem of having independent access and control of two external signal sources relative to the EX88.
Any configuration is ideally done without using switches, but in this case it would be impossible. The next problem is that any switch for this task requires two outputs.
Not many do, and I have not been able to find any that have two RGB outputs.
Also, any sophisticated electronic switches, for convenience purposes often use auto switching, which would be no good for the purposes here.
You need to be able to reliably route signals and know that the outputs will hold.
Therefore I am proposing a mechanical switch unit.
The switch unit I am proposing was designed, as so many seem to be, for VCR configurations... which means their recording output is composite only, as that is all that VCR's can cope with.
However, that would be no good for this application so I am proposing that this switch unit is configured and used NOT in the way it was designed to be used, so that advantage can be taken of its ability to provide an RGB output.
I also mentioned earlier that a compromise was inevitable at some point.
In this case you will have to compromise on quality on those occasions when you are recording from one of the boxes and want to watch the other. Under those circumstances you will be limited to feeding from the box in composite quality only.
The upside is that your recording from the other box will be in good RGB quality.
The switch box is a fairly commonly available unit comprising of four scart sockets. Ostensibly comprising three input scarts [A, B and C ] with a single output scart.
Inevitably the output scart is meant for the TV, and one of the input scarts [A] is designed to be two way in and out for a recording device.
The unit has two switch banks. The first bank is marked A. B and C respectively, and in conventional use which ever of these you press, you get that source outputted onto the TV screen.
However. in my suggested configuration the [RGB] output of the switch unit [ i.e.from the TV scart socket of the switch] is fed to the EX88 instead of the TV... so the ABC switches act instead as selection of the recording source.
In your case only B or C would be used for cable or sky respectively.
The B and C scarts are capable of passing through RGB through to the TV scart [ In this case EX88 scart]
The secondary switch bank has another 3 switches. One is an RGB switch which is depressed when handling RGB signals [ and should therefore be permanently depressed. ] The other two switches are alternate latching types and will switch either the B source to A ... or the C source to A.
You would use those two switches to select which source you wish to watch [ Via the TV's scart input ] when the other source is tied up recording ... but this is the circumstance when it would be limited to composite quality.
You also have the option of watching whatever is being recorded via a high quality route through the EX88 output...which in the configuration shown on the pdf diagram attached is via your scart/vga adaptor in Config 1 and via Component in config 2.
Attached is a two page pdf with two configurations shown.... varying only by the output method used to connect the EX88 to the TV.
You can choose whichever suits your purposes.
The switching unit is widely available.
HERE is one example.
More examples are below. The last two appear to be the same kind of generic switch but in a plastic case which is presumably poorer at screening.
I would also treat as suspect the claim from one of them that it has RGB connections on all three scart inputs. Connections? Probably yes - but routing probably no.
HERE
HERE
HERE
HERE
HERE
Also attached is a pdf with detailed spec of the switch.
Finally the EX88 is linked by an optical lead to your sound system.
One final point. If you are stacking all this equipment I strongly recommend you apply spacers if you can to assist ventilation.
Otherwise heat build up will severely reduce the reliability of your equipment.
[Short sections of plastic drainpipe cut up to uniform short lengths make excellent spacer feet ]