One taxonomy menu using 2 different vocabularies

My problem is I have two vocabularies for each node: topic and tag.
Topic is predefined but tags must be freely written by the user.

I would like to have a menu block that lists the topics and under each topic the tags related to the topic.

So if I have BlogEntry 1 which has topic_a, tag_a and tag_b, BlogEntry 2 that has topic_a, tag_b and tag_c and BlogEntry 3 that has topic_b, tag_a and tag_c, my menu block should look like below:

topic_a (goes to listing of posts under topic_a)
-tag_a (goes to listing of posts under topic_a and has tag_a)
-tag_b
-tag_c

topic_b
-tag_a
-tag_c

So far I tried using Taxonomy Menu & Menu Block, but apparently, it strictly has an option for one vocabulary at a time. I can't combine my vocabularies because one is predefined and the other is freely written, i have to make duplicate tags instead of saying tag_a is a "child" of both topic_b and topic_a.

I've been playing around views and so far I can get to retrieve all the tags "under" topic_a without any duplicates but I haven't found out yet how to retrieve all topics in just one display (instead of creating a block for each topic!)

---anyway, if I do a block for each topic, i still have to found out how to fix the links because by default, it goes to a page of posts having tag_a regardless of topic.

Helpful ideas? Suggestions? Criticisms to how I've been thinking out this problem? :-P Thanks!