Long time ago, read from a fairly reliable source it's due to a limitation in the hardware in the PS3, thus meaning it will never be possible. Of course, according to Sony, decoding onboard makes no difference compared to decoding within an amp (which in theory is true) so not really a cause for concern. At any rate, even after buying the Sony BDP-S550 (for different reasons) I'm wholly convinced it's not worth spending £200 for a light to come on your amp. £350 - £400 maybe (for a much better player).
Each to their own of course.
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