That external devices can buy to convert my digital audio signals into analog audio signals? Perhaps a box or a filter or something. PLZ elements of the consumer good not say that I have something like a keyboard or synth or something, I can insert an analog receiver or any other analog device?

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This is what the converter boxes do that are being sold to watch digital TV on the old analog TVs.  If you can get one of those, perhaps it will do the job you need.  This will make a nice unique gift for you:

RCA Digital-to-Analog TV Converter Box w/remote NEW

US $34.53 (16 Bids) End Date: Thursday Sep-09-2010 5:48:42 PDT Bid now | Add to watch list

Magnvavox TB110MW9 HD Digital to Analog Converter Box

US $39.99 End Date: Thursday Sep-09-2010 6:21:51 PDT Buy It Now for only: US $39.99 Buy it now | Add to watch list

RCA Digital-To-Analog converter Box !!! NEW !!!

US $26.00 (18 Bids) End Date: Thursday Sep-09-2010 7:50:35 PDT Bid now | Add to watch list