Thank you George and MC.
My main question was not about how REAPER works and im not an expert on it at all, it was how the RME UCX works with a signal i feed. You are turning the question to other side. I preffer if you take that time to answer this question http://www.rme-audio.de/forum/viewtopic.php?id=18137
I may have expressed myself badly, but you did your best to understand what you wanted. 24 bits recorded FILES will not have more than 24 bit resolution internally, why would them?. And I know that FILES themselves are not being converted by the DAW, but while they are IN the DAW as soon as i move a fader or call a plugin or something, this file's audio will adapt (or the term you like best) to the software internal's bandwidth. This isn't something special or unknown at all and you can try it yourself freely with this little tool http://www.stillwellaudio.com/plugins/specials/bitter/ and any DAW or plugin. So why don't you answer my question instead of quoting things that i didn't mean?
I will give you a more common scenario, so you don't get lost.
I record audio with a 24-bit ADC. Then i use a software to CONVERT the files to 32-bit (now it has 8 more zeros) and i throw them into any 32bit DAW (say REAPER x86) so this is a nonquestionable 32 bit path (from a file perspective). then i apply some reverbs and those 8 zeros may be filled. What I wanted to know is what happens when this lovely path arrives at 32 bit from a DAW that keeps this 32-bit output (doesn't truncate or dither) to the UCX. How does she handles it?
That was it. You could have guided me here http://www.rme-audio.de/forum/viewtopic.php?id=10617
Im sorry but i felt you were arrogantly avoiding my question.
By the way, i really like my RME interface and I'm fully in love with her.