Indeed, what you see in my previous picture is an extensive improvement for a 203 device. A complete improvement I can say, as it touch all the areas this device it can get improvements (as I know so far...):
-Linear power supply for both digital stage as analogue stage.
-Clock system based on SAW oscillator for main processor, and a precision TXCO for optical drive processor. All powered by battery.
-Fully improved audio DAC board (power system on board, DAC power system, added full balanced stereo XLR outputs, to the existing 8 RCA channels)
-Optical drive mounted on double elastic suspensions, and mechanically stabilised.
-Extended grounding and shielding, as improved ventilation
Answering to your questions...
1. Mainly the modifications for 203 (as pictured) are made on demand. I then use myself the modded device for a short while for testing and some fine tuning reasons. The improvements for 205 model (which I own it myself), are under preparing/development, and very soon available. The already available upgrade for 205 model, the linear power supply (LPM) it can be seen in the picture hereby.
2. The improvements in both cases (203-205) are targeting both picture and sound. Linear PSU for digital stage as clock system improvements it have dramatic impact over the picture quality. The rest of the improvements are directed to the sound quality increasing.
3. A fully improved 203 device working time it may take into two weeks.
4. Yes, it was done it more than once, and the mod approaches it was improved itself since the first modded device. As you can see, the improvisations in this work are mostly eradicated, and particular modules it was designed and produced for upgrading purposes. The overall result is accordingly... The feedback is only positive so far, but mostly in French...
5. An max overall price for a full upgrade (as pictured) it may come up to 1300$.