Well yeah, good point. That would work. You could get the video from the PCE, the audio from the RCAs on the IFU-30, and do whatever you want with it (including combining them into one SCART connector if you want).
I have an SCART-HDMI converter myself, and it has a few millisecond audio delay built into it. This is to compensate for the encoding delay (which is barely noticeable anyway). For that reason, I feed my audio though the encoder. You probably don't need to worry about this.