Again, if his speakers use 3.5mm, he won't be able to USE the Spdif output.
S/PDIF is a digital audio format and not a connection, so I don't know where did you get the idea of 3.5 mm TRS connector won't work on SPDIF.
You may have been mis-informed, also Creative soundcards have been using it for years.
Only thing is, if his speakers does not suppport SPDIF.
SPDIF (Sony/Philips Digital Interconnect Format) is a digital audio format, and is also referred to as S/PDIF, S/P-DIF, and IEC 958 type II.