Indeed. Sistema Aranonera is (partially) documented in the book 40 Grandes Travesias - SWCC did the through trip from T1 to St Elena as documented in this (Spanish) caving club report. Even if you can't read it, the pictures give a pretty complete representation of what's on offer.
http://www.espeleozaragoza.com/Actividades/2010/2010_T1SantaElena/2010_T1SantaElena.htm
The section view on this link will illustrate how small a proportion of the system the trip below T1 includes. You might find the people whose website this is can help more.
http://www.ecgracia.com/Exploracions/Aranonera/aranocavidades.html
On its own, the trip from T1 is mildly interesting, moderately entertaining and not something I'd be desperate to rush back to repeat. It's absolutely fine, it's just not that special; minimal pretties, no mighty lakes, chambers or huge passages and just the one 100m deep shaft to abseil part way down and then traverse across the wall. I think if you head off into the other parts of the system it may get more impressive and the strength of the air blowing out of the St Elena flat out crawl into daylight is very impressive though.
Some fruitless efforts were made into getting access elsewhere but the National Park was either unable or unwilling to help and though this was before the time of everything's on the internet, I don't know that much has changed.
On the other hand, the Ordesa National Park is an absolutely magnificent piece of landscape and it is somewhere I definitely intend revisiting at some point but only for the walking. If you've never been then it's well worth a visit but if you're going just for the caving then you might struggle if you can't track down more information than we did.