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?