If anyone is interested, I have made another recording:
WC2 intro on the Terratec EWS64XL
For some weird reason, I seem to be getting some slight clipping on the EWS, regardless of the volume of the "wave" channel in the EWS mixer. It's noticeable in some places, e.g. "arise, grandson" a few seconds into the audio file.
All in all, the differences seem to be quite subtle indeed, except for the SB 1.5 which is noticeably "brighter" but also contains more audible artifacts ("noisy" playback, clicks and pops). Could it be that the cause of this is simply a low-pass filter that has a higher cutoff frequency or weaker roll-off?