Best path to upgrading older system: Thiel, Adcom, CAL Audio Lab, Thornes....


I've had the same over-achieving  system now for a long time:  Thiels 1.2s, Adcom GFP 565 Pre-amp and 545 Amp, California Audio Lab Sigma DAC with Rotel CD player (and a de-jitter box in between),  Thornes TD 160 turntable w/ Clearaudio cartridge, and speaker cables from Cardas.  Over the years I've gone to high end stores and heard the latest and risibly expensive equipment, which usually impressed me, but not enough to convince me that I needed to upgrade what I had.  My system has always been quite resolving and somewhat hard in the treble when it comes to digital  -- product of the metal dome tweeters on the Thiels, I suspect.  Still, I can't see myself parting with the speakers, which look great in a room that is used as much for entertaining as listening and are very satisfying when it comes to soundstage and rhythm.  I almost upgraded to the 1.7s when they came out, but couldn't quite pull the trigger  I'm a cheapskate, so I'm considering upgrading only the Adcom pre or the power amp.  I listen to a wide range of music -- jazz, classical, rock and hip hop.   It was my sense when I bought the Adcom equipment that the line-stage pre-amp was the greater over-achiever of the two (it also has a nice built in phono), but I wonder, given the need for a seriously powerful amplifier, if I shouldn't upgrade it first.  I'm not looking to spend much more than 2,500, new or used.  Have considered the least expensive pre from Rogue audio, as well as possibly used Ayre or Pass equipment.  But perhaps I should recognize that not much more can be gotten out of twenty-five year old two way speakers, as good as they still are, and buy myself a few engravings by RM Whistler?  
pcln
Um, a new DAC, and also room acoustics. RA can not only tame the Thiels, but also make your room more speaker friendly, not to mention open up the space and soundstage.

I just heard the Rogue tube pre, it's really good.
My dad once owned the 565 preamp which was a really nice piece at the “Time” for the money and yes the phono section was its strong point. I think it’s a toss up on the 565 or the 545 but I’d probably upgrade the preamp first. I think you’ll be surprised how much more revealing preamps are today or even higher offerings of the time of the 565 were such as a ARC LS3 for example. You could mod your amp easily for little money to open up your 545 as those were popular amps in the day to mod. I preferred the 545 over the 555 so you actually have a good amp to mod. If you want to step up and not spend a lot a McCormack DNA 1, preferably a Deluke, will be a nice upgrade over your 545; a much more refined amp.
It really is the most sensible thing to look at upgrading your speakers before trying to make new gear make the old ones sound like recently developed technology. It's a hard step and you can keep the old ones when pangs for nostalgia hit.  Once you've decided on new speakers match the rest of the gear to them.  That may seem simple at the dealer who might be demo-ing gear more expensive than you can afford, and your speakers can become seemingly mismatched orphans for some time.   I had such an experience but eventually did find the right amps and sources for a very good system.
Agree to change the speakers first but if you’re happy with your Thiel’s then preamp. Been a long time since I’ve heard a pair or 1.2’s but I recall they were nice at the time. 
Get an integrated with a built in D/A.  There are many options.
Many thanks for this reasonable responses; I'm not only loath to replace the Thiel's because they look good in the room but because I have yet to hear anything their size that actually appealed more to me.  The Thiels are able to do a bit of what good monitors can do, without all the fussiness of stands.  I may try to get my hands on a used McCormack power amplifier -- and perhaps the Rogue preamp as well. 
The pre and power amps you suggested are good choices. You should probably change to a more modern DAC. They have come along way since the Cal. Maybe consider a Node 2i streamer and Tidal subscription??? Thiels are good speakers.
pcln
I saw Thiel cited in your system as above. Please join us over on the Thiel Owners thread. I would be interested in learning more about you and your musical tastes. Good to read that after 25 years, the 1.2 , still engages.  Happy Listening!
Have fun !
enjoy the music
+++ for anything Rogue makes