I recently found these two very interesting PDFs, which seem to be the official ensoniq technical information about their es1371/es1370 soundchips.

es1371 - Google HTML
es1370 - Google HTML

According to these documents at least the es1371 based cards (used in later SB 128 PCIs; see here) seem to resample all audio input/output to 48khz.

dev0

This appears to be (in the case of the 1371) a document for the Ensoniq AudioPCI 97 card, containing a 1371 chip. Here's a quote:

"AudioPCI 97 is the new ENSONIQ AC97 digital controller which provides the next
generation of audio performance to the PC market. AudioPCI 97 is a 5.0 Volt PCI bus compatible device that enables the ENSONIQ SoundScape PCI solution. AudioPCI 97 along with an AC97 CODEC..."

Since this card was an AC97 card, I'm not surprised it resamples to conform to the AC97 specs. I don't understand how this suggests the SB PCI128's which use the same chip (unless CL modified it since then) are required to resample -- They certainly could, if following AC97 specs.

Perhaps I'm missing something here...

Any card with a 1371 or 1373 will resample 44.1kHz to 48kHz audio, because those chips are made to connect to AC97 CODECs which only take 48kHz audio. They have an AC97 controller built-in, so AC97 CODECs are all they will ever be connected to.

Nice thread resurrection... I'll take your word for it. I don't recall hearing any difference when using software upsampling, but maybe it wasn't audible through the speakers/headphones I was using at the time... or the resampling is just done well in the hardware.