My Terratec is ALWAYS at 48 kHz which is not bad but as I always have to resample the rendered wave. I cannot reduce the sample frequency in Renoise. Neither 1.8 nor 1.5
Terratec drivers have specific issue, but usually they are all ASIO related.
Usually “Only 48Khz” also means the samplerate is locked in the soundcard configuration (no matter if this is ASIO or DS), if you lock it to a specific frequency, no other frequency becomes available to Renoise.
You are sure that you haven’t done this?