str 343s
I did some quick searches. It looks like you have a model that was only release in Europe. I'm guessing someone from the Armed Forces brought it back with them sometime before you picked it up. Does it happen to be set up for 220v input instead of 110 ? or perhaps the voltage has a select switch ?
The model is not showing on the Sony main database... The closest they have is an STR-333.
In general, though, the 300 series is their "baby" line. It steps up to 500, 700, 800, and the "top" of the mass-market stuff at 900 series. Their higher end stuff is generally in the thousands (ie STRDA2000ES), with the notable exception of the well-regarded STR-DA4ES, 5, 7 and 9 models of a couple years back.