What bitrate is downmixed DTM?

[Superwof]

Maybe this question has been answered before but I have not been able to locate the appropriate thread so let me just ask this:

The Toshiba E1 is able to downconvert DD+, DTS-ES and Dolby TrueHD to plain DTS and output this signal by SPDIF. I now wonder what bitrate this signal might have. Is it 48khz @ 640kbps or 1.536kbps? If limited tos 640kbps, is this then caused the SPDIF's max. bandwidth or is it a limitation within the plain specs?

Im awaiting arrival of my E1 this week, however have a now 8 year old Sony receiver and wonder if to expect any compatibility problems when hooking it up....