Yes i see what you mean. I don’t pass the sound through the XRGB-3, only the video goes there and only via the 15 pin input on the back. I don’t use the JP-21 socket on the front.
All my consoles are connected via either original SCART cables such as the Playstation, Saturn, MegaDrive 1 and 2 and Master System 1, NEO-GEO AES and CD, or custom SCART cables, in the case of the Master System 2, NES, Sanyo 3DO, and Atari 2600 RGB mods i have those configured to use the NEO-GEO original SCART cable, the SNES and N64 use a genuine Nintendo JP-21 RGB cable that i modified to be standard SCART pinout. The Dreamcast connects direct to the projector via RGB-HV from a custom cable.
All the different SCART cables go into a few high quality SCART switchers that have a full disconnect of all pins via latching switches, linked together using high grade custom shielded SCART cables i made up, then off to a SCART breakout board that outputs RGB-HV via both 5x BNC sockets or the 15 pin, and from the 15 pin goes direct into the XRGB-3.
From there, the 15 pin output of the XRGB-3 breaks out into 5x BNC and runs up to the projector via 5 equal length RG-6 coax cables into the 5x BNC sockets for RGB-1 input on the projector.
I have tested with no SCART switcher, and did test looped through up to 7 of them, and there is no change in signal quality that can be seen on the screen. Generally there is 3 SCART switchers, and the 3rd in the chain is hardly ever used. Obviously when they are not used the switch on the next one is electrically isolating it from the chain, so there is no loss or interference there.
The audio goes straight into the AVR, either direct from the stereo output on the console, or out of the last SCART switcher via the RCA sockets they have for audio break out.
Though even still, the AVR has a number of digital audio inputs if i ever did need them. The WiiU goes direct into one of the HDMI inputs on the AVR and the Wii connects direct to the AVR via a component input. The Faroudja scaler in the AVR is set to pass through because it adds noticeable lag. The AVR has an HDMI cable going direct to HDMI-3 on the rear of the projector, and being a CRT projector it does not need to scale any resolution (provided the signal is above 31kHz) in such a way as a fixed pixel digital display does, so there is zero lag there.
I do very much like the look of the OSSC, it appears to do everything i use my XRGB-3 for, and appears to do it all very well. It is an impressive device with a lot of capability.
The projector did have an internal LiMo PRO scaler (an optional extra on all the later model Barco CINE series CRT projectors, slots in the card cage) that is capable of line double, line triple, and line quadruple, as well as scan double and de-interlace, which does actually work incredibly well and added no lag, but there is no option to dim down every added line like the scanline option in the XRGB-3 and OSSC so it does tend to make the image look a bit blocky.