Upgrades for Thiel CS 3.6?

I have a pair of Thiel CS 3.6 that I’ve owned for about 12 years. I think they’re fantastic. 
Just curious... have there been driver advancements that I might benefit from? 
Has anyone tried swapping out drivers and if so, were you pleased with the results? 
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@gpaulmg, Rumors persist that ex-Thiel guys are working on upgrades. Perhaps we'll know more when the Thiel Audio bankruptcy proceedings conclude. 

unsound is correct...there are literally hundreds of posts in the Thiel Owners thread regarding all the work being done on mods & upgrades for legacy Thiels. Preliminary projects are offering replacement crossovers that feature top-level, modern components & construction, as well as sourcing modern driver components that will match the voicing of our existing speakers (I have CS 3.5's) as much as possible.  These projects have former Thiel employees & leadership behind them, including Jim Thiel's brother, Tom.  As unsound said, the resolution of the Thiel Audio bankruptcy has a lot of things in limbo, but in the meantime, Rob Gillum (who likely help build your 3.6's) has opened Coherent Source Service near the old Thiel factory & can help with repairs/parts/service should you need them.  

Hope you & yours are doing well...

Lots of good points above. I’ve got some 2 2’s, once I matched them up with the correct components, I never wanted to change them out. Had them since around 1993.

My epiphany came by not matching them with a high wattage amp(s) (oh, the watts), but gobs of current. This is probably why a lot of Thiel owners settled on Balanced Audio Technology back in the day. Matched with the optional bat paks and six paks (oil filled capacitors) I found an ease and sweetness I’d been lacking. And the soundstage, oh my.

I plan to check into the current components and upgrades being discussed on the Thiel group. The 3.6’s are a speaker you could keep for a long, long time given the room to breath and the right electronics.
FWIW I have CS6's. Here's a few more points:

If you are interested in learning more than you ever wanted to know about Thiel speakers I recommend that you read the Thiel Owners thread on this forum. It takes several nights of reading but you will come away with a new appreciation for your speakers.

The main defining characteristic of Thiels is that Jim used first order crossovers on all of his later models. That means that each driver has to operate over an unusually broad frequency range which is a hard thing for a driver to do. By the time your speakers were produced Thiel was completely using custom drivers - many of them manufactured in house. This design decision was due to Jim's belief that phase and time coherence was critical to getting accurate sound.

For the reason above you will not be able to find non-Thiel drivers that will work in your speakers. They simply are not designed to work over the frequency range that Thiel designed his drivers for. The only company using first order crossovers that I know of is Vandersteen.

Regarding amplification I run a Krell KSA 300S which doubles power down into 2 ohms. You'll see in the Thiel thread that the company used high current amplifiers like the Krell to drive their speakers. Other users report good results with less robust amplifiers but I believe that one of the reason my CS6's sound so good is because my Krell can handle the difficult impedance curve with ease.

Rob Gillum, a former Thiel employee, has started a company called Coherent Source Service to repair and maintain Thiel speakers. I blew one of my woofers, for example, and Rob was able to rebuild it. He does have some hot rod crossover kits for various models but I don't know if the 3.6 is one of them. Before you email or call him you'll need to get the serial numbers of your speakers so you can let him know that info. I would ask him about the brightness you experience and see if he has any suggestions.

It's going to be really hard to improve on your 3.6's. I went to AXPONA and the Florida show a couple years ago and I came away amazed at how well my system compares to most of the megabuck systems. The one set of speakers that really impressed me (MBL 101E Mk II) were $70K. I won't be buying those anytime soon.

Finally, the brightness you are hearing may be an issue with room acoustics. It doesn't take much flutter echo to affect the sound. Also, you might be experiencing the effect of early reflections from the walls, ceiling, or floor. If you haven't done some serious work on your room I would work on that before messing with your speakers.
There is a drop-in replacement soft dome tweeter diaphragm available for the 3.6 tweeter.. The 2 user reviews are very positive. One reported an improvement after it broke in.

Scanspeak dome assembly D3004. (the 3.6 uses a Vifa D26AG36-04 Tweeter but its a drop-in replacement coil/diaphragm with no mods needed)

That said I still wouldn't mess with them,  as stated in the post above Rob at Coherent Source might have a proper mod.