Latest Transmission is in experimental distro, here is a way to get it.
First you have to add sid and experimental distro to source list
echo "deb http://ftp.debian.org/debian/ sid main" >> /etc/apt/sources.list echo "deb http://ftp.debian.org/debian/ experimental main" >> /etc/apt/sources.list
You can modify the source url with your country code to speedup.
Do an update and install transmission
apt-get update apt-get -t experimental install transmission-daemon
Now you have the latest transmission.
You'd better restrict other packages to stable distro.
echo "APT::Default-Release \"stable\";" >> /etc/apt/apt.conf.d/71distro