I personally think that 08 XKR rear end looks blah, not aggresive at all. A rear valance would really add to the look.
I have searched , but cant really figure out if a diffuser out of XKRS fits and XKR.
I Think this would look pretty good and have seen an identical spoiler at the dealer on an XKR https://www.google.com/search?q=xk+s...SAOnie0fCiM%3A

 

The rear bumper and diffuser of the facelift 5.0L cars (i.e. a 5.0L XKR-S) is different to the 4.2L cars. I don't think the 2012 XKR-S diffuser will be a direct fit to the earlier XKR rear bumper.

There was a 2008 4.2L XKR-S however... but according to the parts catalogue it also has a different rear bumper to a regular 4.2L XKR...



The 2008 XKR-S diffuser does still look a little plain compared to the 2012 XKR-S one...



But you can see they are a different design completely.

 

Hmm,, the rear bumpers on 08 KKR KXRS and new 12 XKR look the same at least to the eye..
I have examined my stock rear bumper and I noticed extra hole on left and right side on top of the bumper above the exhaust tips, indicating they are possibly used in another application such as maybe an KXRS rear valance?

 

There is no difference that I know of and the R-S 3 piece lower valence kit will fit.

 

Could well be then, they have different part numbers though...

 

I have an 07XK (4.2) and the rear valance was certainly needing a bit of an upgrade. I went with the option pictured. Relatively cheap compared to many others and it does a good job of replacing basically a 'flat' panel on the XK. I just snapped a picture with my phone, and yes, it is quite dirty….. lots of rain and slush here over the past few weeks. I put the dual tips on the muffler to complete the look.
About 15mins to install



At first I had it painted to match the body then went to black

 

So the reason you're out driving in the rain and slush, is because its cheaper than keeping the car in the garage and feeding that parking meter?

 

LOL….I have a few cars to pick from but I still drive the XK at least once per week…. yes even in the snow. As you can see from the pics, I have snows mounted on the spare rims. Parking meter on one side and on the other side theres a gas pump… still can't get any gas out of it though!

 

Powerhouse started a thread on this back in 2015 think Chris from mina gallery was the man to speak to .

The other option that was suggesting was the valance from Priince (Fstbmw1)

For a third option you've got prior design fellow member bighenderson had the whole kit fitted at one stage

 

This is the rear bumper/diffuser from F/X Designs. On ebay and on their website the diffuser part is shown both in the body color and in the matte charcoal. I chose to paint it all one color. I also replaced the black plastic honeycombed mesh with a stainless mesh that I put together from two mesh grills from Mina Gallery. Just a little different look that makes it my own.

 

All rear bumpers are the same from 2006-2014, they only changed the valance on depending on the different models. I have a 5.0L XKR valance on my XK fits straight on.

Its just bolts and clips, the bolt holes for the differing valances are all pre-drilled.