I've had my 4BSST2 since getting Thiel 3.5 speakers (now Thiel 2.7s). I got a BP-6 early on, and, for years, the 6 and 4B were it. I bought a 17cubed last October, and am really happy with it, although it took about two months to settle in with the 4B. (wonderful mids and highs)
Now, I'm putting together a system for my son, using a 4BSST2 I picked up on eBay and a new BP-26. I'm using my speakers and an old pair of AR3a speakers while I look for a pair of Thiels for him. Switching between my old BP-6 and the new 26, I can certainly tell the difference, as the 26 sounds more dense and with a pronounced lower mid range. (Strange, as the 6 and 26 have the same basic amplification circuitry.)
As you, I leave my preamp, amplifier and CD-3 spinner on, 24/7.