Find a used Monarchy Audio "Dip SuperDrive". The Dip Superdrive has a 3db boost for the signal on it's BNC output that is designed to handle runs up to 100ft. You can use a simple 10ft inexpensive toslink from your transport into the Superdrive Dip and use the best BNC to ? dig cable you can afford and mates well for your situation. Another option is to use a long (7m) toslink from transport to Superdrive and a very good BNC to ? from the BNC out from the Superdrive to Dac. Another option and best is to use 2 Superdrives and keep the last Superdrive close to your Dac. A very good dig cable is the Kimber Select KS-2020 but as always you need to try yourself for compatiability and personal taste. Look up Monarchy Audio's telephone # in the Manufactures list and talk to the owner C.C.Poon. C.C. will tell you what should be best. Good Luck ....
