Have you got a link to the ebay DRL kit please? Might be an interesting upgrade, i made my own using switchback combined DRL/indicators LED bulbs for my 827 Sterling, quite a game as the indicator lamp units have a removable orange lens inside so had to strip and rebuild them.
Hmmmm, i really want to get a longer beam as well as actually having illumination of the road in front. I know on both my Volvo 760 and Rover 827, the beam distance improved with H4 LED bulbs so i was kind of hoping the beam distance would improve on the S Type too. On the Volvo, because the reflectors were tarnished (they are 35 years old this year so are allowed to be! 😛 ) they wouldn't actually give a definite beam pattern on filament bulbs, it was only just good enough to get a pass on the MoT but the tester muttered about poor beam pattern, not likely to pass next year (that was 7 years ago and had LEDs in since) but the Rover had new headlights and both gave an improvement on beam length.
Because of my experience with both cars and doing the outer beams (dipped and main combined on the H4) both got inner beam improvements too, the Rover got some el-cheapo "Chinabay" H3 LEDs that used COB LEDs instead of the better Lumiled type used on the H4 jobbies. This resulted in no beam pattern at all on the inner beams but because they were so bright (something like 10000Lm if memory serves, might be 6000Lm per H3 LED bulb) switching to main beam is like turning the sun on.
The Volvo got 35W HID conversions for the driving and fog lights, both inboard of the outer combined dipped/main beam lights. As it's a 1988 car the MoT testers pass it anyway because it gives all correct beam patterns. Not had a problem with the Rover either but that was before they changed the law and i changed MoT stations thanks to the previous one bodging a repair on the Rover and making it unsafe to test, never mind drive!
For now in my S Type i have some cheapy ebay "Xenon look" halogens that work well - normally! Although a vast improvement on the original (nearly black so probably original to the car) bulbs, still not great especially at dusk. Having been used to LEDs for so long on my other cars as soon as i get the Jag in for MoT (and hopefully through it too) i'll be getting some LED H7 and also HB3 bulbs for it.