I went with the AeroCoach titanium Ascalon extensions; I just loved how clean their SLR-specific adapter is. Looks OEM.
Here's a bunch of pics of my 2023 SC SLR just built mid September.

It's a SLR 7 Ultegra build Project one with Full Fade paint scheme: Rage Red > Deep Dark Blue with the logo in "brushed chrome".
The colors are hard to render in picture - looks better in person.

Here's a couple of pics the bike shop posted after the build (but before setting my fit on it and before my tinkering).
The Pro 51mm wheels will be for training.





This has been an expensive project so far as this is my first Disc Brake bike and therefore none of my existing race wheels are compatible, had to figure out a power meter solution too as I was using Powertap Wheels. I stopped counting. Especially knowing this bike likely won't be much faster (if at all) than the Gen2 SC it replaces haha! But nice to sport a new ride.

Also planning to go Tubeless after swearing for years I would stick with Latex.
Ended up getting a Stages LR powermeter on a Dura-Ace crank I sent in for 'factory install'.

First upgrade was the saddle - went with the Wove v8 Saddle and so far love it (I plan to post a review on their thread when I have a chance). It's mind-blowing light :)
Also love the built-in bottle mount. I played with it and 2 bottles is possible.



I was not happy with the Aerocoach accessories for the Garmin and bottle mounts.
With my old eyes, I need big numbers and I use a Garmin 1040 computer, too big and heavy for the 3D printed mount they provided held by a single bolt.
The extensions are quite close from each other (or quite far if inversing the adapters) and the larger Garmin did not fit well between my wrist. Plus it was vibrating due to the heavier weight.
Also wanted both the Garmin and the BTA bottle in specific spots to make the best use of the available space.

I also did not like their carbon fiber sheet being mounted between the SC adapters and the bars. Looked funny. So I made my own (larger) carbon fiber sheet that mounts between the bars and the arm cups and is used to mount and locate both the BTA bottle and the Garmin computer (see later pics).

I also designed some bits to me made in Aluminum and tried to find a local shop to machine them, but this ended up way to expensive for the quotes I got especially not knowing if I would be happy with that setup..
So I just got aluminum bar stock online for a few bucks and hacked my own using an angle grinder, a drill press and some taps;
Result below.. I found a local shop that anodized them in black after the picture for $30 each.
- The threaded bottle space is not used in the following pictures but I can insert it below the 50mm BTA spacer to raise the BTA bottle further if needed.
- The other part is to replace the first piece of the articulated Trek SLR garmin mount (made by K-EDGE) so I can mount it to the carbon sheet I made and also position the computer exactly where I want it.



Here's the bike as it stands now;
I did take the aerobar angles from the native 21 degree down to 14 degrees using the -7 deg Trek spacer based on some comments in recent videos and past ST threads for aerodynamics.
But only way to tell which is best would be aero-testing; I do have the hardware needed to go back and forth.

After a lot of indecision for a rear disc, I ended up getting a Swiss Side Hadron Ultimate disc. Same exact disc as the DT SWISS one but a bit cheaper.
(ordered without stickers). I do not have a front wheel for racing yet, I just ordered a Vanquish Pro RC 60 with the Black Friday deals.











Here's a good view of the cockpit customization with the carbon sheet holding the bracket for the Garmin computer and the BTA bottle spacer.
All screws are titanium, the whole setup is quite light!




This maybe shows better the color fade; In most pictures the dark blue appears to be black.



This bike is also my first bike that does not have 2-button shifters, can't say I like being forced to the 'synchronized shifting mode' - I do not like it so far.
I got the parts to add satellite shifters to switch back to "manual shifting mode" for the FD - but I have yet to see if I can fit them in a clean and ergonomic way to the brake levers.

As I got the bike in mid September and passed more time tweaking it than actually riding it before the weather got too cold (to my taste anyway) to ride on the roads, I do not have many rides on it yet but looking forward to next spring.

(Is that enough pictures?) :)

Just curious - is it possible to get this down to 7 degree tilt ? Their website says u can use the trek adapters to get to 14, but I like a bit flatter.

I have seen someone selling the Ascalon extensions like you have. No mounting hardware for the trek though. Was going to pull the trigger but these seem to revolve around a lot of tilt ?

Anyone had creaking apparently coming from the IsoSpeed? Mostly happens when sitting (not in aero position) when more weight is on the saddle. Drives me nuts though, a little creak every pedal stroke. I like my bikes dead silent, just a little purr from the chain and hissing from the tires :)
Bike has only 300 miles (but has been sitting in the basement all winter).

Maybe all it needs is a bit of lube...
Service manual seems to bring caution to only have it serviced at an authorized dealer though; Anyone here yet took the whole thing apart and re built using the manual's instructions?

Did you get this sorted out? Mine is creaking and getting louder and louder. My trek shop won’t service it and want me to bring it elsewhere even though I bought it from them. I could do it myself, but like you said, the service manual says not to.