I also found a cable to connect a pronto to a AV device. It is explained that the Pronto outpus 2.5V, and the AV-receiver inputs 5V (the cable make the conversion):

[Link: cgi.ebay.com]

Does it mean that the above cables are used on 5V systems? So, the Pronto won't be able to drive 2 serial leds; they have to be connected //...

And what about the wave length? Are all these cables really universal regarding this point?