Maybe the times when the sound disappears is when the Hummy is switched to 'mute'. This does affect the sound on the SCART passthru, for some reason.
When an upstream device first switches on, it overrides this and so sound will then be heard. If the Hummy starts a new 'event' like starting a recording, playing back another one or being switched to another channel, an 'event' is generated, and the Hummy takes control over the sound output of the SCART again depending on the 'mute' setting.
I have had my 9200T for a couple of years, passing through a Philips DVD Recorder (formerly a DVDR-610 and more recently a DVDR-5550), and from there to my TV (formerly via SCART to a 1997 Philips CRT model, and latterly via HDMI to an LG 37" LCD model) and have never had any problems, and have never had the need for external SCART switching.