Hi,
My first message here.
The new grundig S450DLX is not a new version of the S350. The S350 was a Tecsun, the new S450 is a Redsun. Exactly a Redsun RP2000 or RP2100, the version with memories I think, but in new habits. Seen elsewhere : not only the case is new, but there is a better loudspeaker than in the Redsun. But all radio specs are the same.
For the SSB decoder, I remember an accessory named TG37, seen on the Internet. I think this is no more than an external BFO. But it was with phono (RCA) plugs, and the S450 has F-type sockets on the rear side.
So, you'd better think to use the 455 kHz output with a downconverter to 12 kHz, and then to a PC soundcard: that's a very cheap SDR (with free software decoder of course).
I don't understand why this "new" model is late. Maybe too much S350 still in stock ?
Ray