I have owned both the 508-20 and the 508-24. The 508-24(not an upgraded 508-20) sounds a little better. I can't say it is actually more open but it seems to come from a quieter background. I think the dynamics might be just a hair better overall. As for the transports, they sure seem to be alike but I've never looked inside. They function exactly the same(takes a few seconds to initialize). Is it worth a $700 upgrade? Good question. If you're looking for the best in absolute terms---yes it is. Can you be extremely pleased with the 508-20---darn straight. I've noticed the prices on Audiogon for the 508-20 have gone up a touch. They use to be in the $1000-$1100 range. Now it looks like $1200-$1400.
Might sell yours and catch a mint 508-24 for about $1800. Just a thought.
Might sell yours and catch a mint 508-24 for about $1800. Just a thought.