More links with news about this:

http://www.naiz.eus/eu/actualidad/noticia/20141218/la-an-envia-a-prision-a-siete-de-los-detenidos-en-la-operacion-pandora-y-les-acusa-de-ataques-que-no-menciona
http://www.elperiodico.com/es/noticias/sociedad/prision-para-los-detenidos-operacion-pandora-3784221
http://www.eldiario.es/politica/Prision-detenidos-Pandora-atentados-artefactos_0_336317428.html
http://www.nodo50.org/cna/?p=3252
http://politica.elpais.com/politica/2014/12/18/actualidad/1418928458_391774.html
http://es.contrainfo.espiv.net/2014/12/19/estado-espanol-acerca-de-la-operacion-pandora/
http://arainfo.org/2014/12/el-juez-gomez-bermudez-envia-a-prision-a-siete-de-las-personas-detenidas-en-catalunya-en-la-operacion-pandora/

The book they are "accused" of reading is called "Contra la Democracia"
(against democracy):
http://gci-icg.org/books/Promo_ContraLaDemocracia.pdf
(that's just a promo)

Haven't seen any reasoning as to why Kasa de la Muntanya was raided
since no arrests where done there... (stronger support for opportunity
raid theory)

Regarding the people sent to jail... evidence seems to be mostly missing
and yes they are talking about they where using riseup, or having copies
of that book. One of the sources says one of them was found street
fighting gear, knives and golf balls (el pais). Strangely El Pais seems
to provide much more information than other papers but they're still not
providing much more than narrative... for those not in the knows most of
the sources up there are counterinfo but some are more "mainstream"
specially El Pais (used to be serious, but nowadays mostly government
voice) and elperiodico (i believe this is more serious).

Also, some of the sources mention this comes from some other raid from
time ago on two people that where accused of planting a bomb in
Zaragoza. Now they have used whatever they got then to lead on choosing
a few more targets, going for these 11 citizens, kasa de la muntanya and
other anarchist social centers. To me it looks like the "authorities"
are just looking for more deniable leads to follow for more attacks.

Also funny coincidences, on the same day the former president of
Catalunya (Jordi Pujol) was officially accussed of corruption (too much
money in Andorra), and also the Catalonian National Audience was set on
fire (that points to proof destruction).

Kisses!