At 44.1 kHz, for the usual cable lengths of 3 or 6 feet, any decent-quality RCA to RCA cable will do; special "coax" with 72 or 75 Ohm characteristic impedance isn't needed.
It's a matter of signal wavelengths. When a cable is less than about 1/8 wavelength, its characteristic impedance doesn't matter enough to worry about. At higher sampling rates, the cable's characteristic impedance begins to matter at correspondingly shorter connection distances. At lower sampling rates and with relatively short cables, it's simpler: You only have to care about making a good electrical connection.
So don't get all attached to any one special cable because you paid extra for it and/or have been using it a long time; just switch to any other well-made cable in good condition that you have, and it will very likely fix the problem.
--best regards
P.S.: S-P/DIF signals use the same bit assignments and the same bit rate (for any given sampling rate) whether 16-, 20- or 24-bit signals are being sent. If you send a 24-bit signal to a 16-bit receiving device, the receiving device simply ignores everything beyond the first 16 bits, effectively truncating the samples. That isn't good audio practice (you'll get granular noise on low-level sounds, so in this situation a dithered 16-bit signal is called for), but the connection itself is entirely workable from a data transmission standpoint.
--It's been years since I looked at the standard, but if I recall correctly (and that's becoming an increasingly dangerous gamble as I get older), S/P-DIF as opposed to AES/EBU may only use 20 data bits per sample at a maximum anyway, with the lowest-order 4 bits of 24-bit sample values being thrown away in effect. Maybe someone here who's read the standard more recently can confirm or deny that. ISTR that the lowest-order 4 bits are transmitted separately in AES/EBU (which really does treat them as data bits) while those particular bit positions in S/P-DIF are assigned as unused flag bits for future expansion or the like. OTOH the manufacturers of receiver chips could perhaps bend the standard and recover those bits.