Need RCA to XLR adaptor for digital cable.Help

You might try the Monarchy DIP, which is sold on the "tweaks" section of Audiogon for $185. Its main purpose is to reduce digital jitter, but it also will convert a SPDIF to an XLR signal. You just plug a SPDIF cable into one of the units inputs and an XLR cable into one of the outputs.

Audiogalore, I agree it is not ideal but if the OP needs to do it, it will work and he may or may not hear a degradation.
Some do, some don't.

Should never convert digital transmission XLR TO RCA or RCA to XLR.

The digital cable is high speed transmission and has shield connection on both ends designed to help build RF/EMI.

You can however use this application in a analog stage,because a properly design analog is only shielded at one end to ground were the other end is open and wrapped around the conductors.

Providing to you pay attention to the direction arrow on the cable and make your conversion at that end of the cable.

Hope this help clear some thoughts about this type of conversion.

Enjoy music!

Look on Benchmark's website, Canare makes a converter that will match the impedance, costs like $30.

Yes, something like this SPDIF to AES/EBU converter, costing $90, is probably the best way to go:

http://www.bhphotovideo.com/c/product/395533-REG/Hosa_Technology_CDL_313_CDL_313_Data_Link.html#specifications

However, if your Fostex is a CR500 or similar model, it claims to be able to auto-sense whether its input is SPDIF or AES/EBU. SPDIF (which is what is most commonly transmitted via 75 ohm coaxial cable terminated with rca connectors), and AES/EBU (which is usually transmitted via 110 ohm twisted pair cable terminated with xlr connectors) differ in terms of both impedance level and voltage levels.

I don't know whether or not the Fostex, when it senses SPDIF, will adjust its impedance level to 75 ohms. If it does, you may be able to get away with a simple rca-to-xlr adapter such as those you referred to. Especially considering that you are not going into a dac, which makes jitter less of a concern. If the Fostex presents a 110 ohm input impedance regardless of the signal type coming into it, then you almost definitely need a format converter such as the one I linked to.

Regards,
-- Al

Look for one specified as and AES/EBU to RCA adapter.