The best ST-140's were the very first models made. These were only rated at 70 wpc and had iron core ( old style ) transformers. The second production models were rated at 105 wpc and used toroidal transformers (wire-wound "donuts").
As such, the older B & K amps are soft and smooth, erring more on the warm and mellow side than on the hard or bright side. As such, they are typically more listenable with digital sources than many of the other amps that are currently available. While not anywhere near the last word in detail or resolution, it would be hard for someone to find them as being "offensive" sounding.
Given your speakers and the use of metal domes, it would be a FAR better match (in my opinion) than an Adcom, Acurus or Parasound product. On top of this, you can typically find these for well under $250.
One thing to remember though is that some of these amps used output devices that are no longer currently available. MAKE SURE that the amp is fully functional and that they guarantee it to be working upon delivery. Should the amp take a dive, B & K will rebuild it to current production standards for a VERY reasonable price. Sean