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
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