As an owner of the 31SE, and a long time owner before this of an ARC LS5, etc., I can not imagine the SF preamp "easily running circles" around the 31SE. In the mid 90s, I tried the SFL2 for a 3-day weekend audition and it was hands down the most boring and lifeless tube preamp I had ever heard. Contrary to the Stereophile A rating of this, the SLF2 was not musical at all. Perhaps SF's later products, the "Line" series, have changed all this. But unless anyone here has heard the 31SE, it is not fair at all to base its ability on its price. As much as I like ARC products, BAT gear slaughters ARC in the value dept. You simply get far more of a product for the same or less than the ARC equivalent. And as much as the LS5 was vastly superior to the SFL2 at the time, I suspect the 31SE could do the same to any of the last SF preamps. And if you want warm sound, if the latest SF products are at all like the SFL2 was, oh man, you can forget about a warm sound altogether. Used products like the ARC LS5 or BAT 31SE are in a different league. One note: the BAT 30SE is really not in the same league here so focus on the 31SE. And if you want a unit built like a tank, look no further than the BAT units. Their power supplies are incredible and much due to their success. So go listen and determine this all for yourself.
John
John