Reddit reviews Microsoft XBox High Definition AV Pack

Yup, I had an early HD RPTV that would accept 1080i signals over Component video. Pre-HDMI as you mentioned.

OG Xbox could output 1080i over component as well, as long as you had the HDTV AV Pack.

Also, wow they want a lot for that thing. Glad I already have one!

if it helps, I have a 20L5 and over 30 consoles and here's what I did.

• SCART Breakout cable from retrogamingcables.co.uk for the 20L5
  
• BKM 129X additional card for your 20L5
  
  The reason for the two is I split everything into 2 categories
  
  
• 1 - RGB SCART into the built-in inputs on the 20L5
  
• 2 - Component (YPbPr) into the added 129x card
  
  All RGB SCART consoles are being handled by a 'gscartsw' (scart switcher)
  All Component consoles are being handled by a an 'Extron Matrix 300' (multi format switcher) get one cheap on eBay
  
  
• Original Xbox - OEM Component Adapter Xbox HD AV Pack Do NOT get 3rd party cables, you will easily see how bad they suck with a monitor such as a 20L5
  
• PS1 - RGB SCART Cable (ordered from a polish modder on eBay but retrogamingcables in the UK or wookiewin in US are good too)
  
• PS2 - OEM Component Cables these NOTE because the 'gscartsw' can't handle sync on green I elected to go with component instead. Again stick to OEM for same reasons OR HDRetrovision's cable. They are fairly new.
  
• Sega Genesis - RGB SCART - get the right model (1 or 2) from retrogamingcables or wookiewin
  
• SNES - RGB SCART - same place as Genesis - try and get a "1CHIP" version of the console OR get a SNES Jr/Mini but this one will need an RGB mod as it doesn't do it natively but with this chip here it will look incredible. This is what I have and HIGHLY recommend it.
  
  When you're ready to handle the audio now let me know and will tackle that!
  
  
  **edit forgot to add, some sellers market PS1/PS2 RGB SCART Cables as the same or interchangeable but they are not. They will either have no resistors, 400ohm resistors or 1000ohm resistors. The PS1 needs resistance but the PS2 does not since it is built into the console. So:
  
  
• PS1 requires 400ohm resistors in the SCART Cable
  
• PS2 requires NO resistors (built in console)
  
• Some makers make a 1000ohm SCART cable that can be used for BOTH
  
  Check the descriptions of the cables for this info or ask the maker if it's not printed.
  

Edit2: I'm a dumb dumb. I have been learned that the OG Xbox is limited to 480i on over SCART cables. There may be some use cases for this and emulating some older consoles. But the best video output option is definitely via the original HD AV Pack (https://www.amazon.com/Microsoft-XBox-High-Definition-AV-Pack/dp/B00005R6YZ) into a high end upscaler (OSSC). 480p, 720p, and 1080i are options available over component, depending on the game.

Another option is to use a SCART cable and get an OSSC if money really isn’t an option. Probably the best possible quality you can get. Might be tricky to figure out how to get 5.1 working. No idea if there is such a thing as xbox SCART cable with optical audio.

Edit: you can mod your Xbox and add a digital audio output port fairly easily if you want RGB and surround video output.

So this SCART cable:
https://www.retrogamingcables.co.uk/xbox/ORIGINAL-XBOX-RGB-SCART-PACKACPUNCH-PRO-CABLE

This digital audio mod:
https://m.youtube.com/watch?v=1uGUSwMKhKo

OSSC to convert RGB SCART to hdmi:
https://www.videogameperfection.com/products/open-source-converter/

Best possible everything you can get. Is it practical? Ehhh not so much. Although I just bought an OSSC and about to pull the trigger on the SCART cable. Planning the digital audio mod as well. If you have time to wait, I’ll do a full review.

I bought a component cable before I realized that THESE exist. The component only improves color slightly while the HD pack can upscale to 720/1080. I haven't tried it, but here is a link to where I read:
http://xbmcxbox.blogspot.com/2013/04/play-original-xbox-games-in-hd-high.html