you could do it the way you tried, but that's overly complicated. What you have to understand, is that the rss feed manipulated is an XML file. so, what you're trying to do using a regex, you can use the rename for that.
To put an example on my words:
in XML file / the language you tried addressing in your regex: <sub-sub-item1-1/> <sub-item2/>
is equivalent, using item structure in pipes, to: item.sub-item1.sub-sub-item1-1, item.sub-item2
that way, getting the content of href of item.url can be done in one step using the rename: item.td.0.a.href [copy as] url, and the title in the span using item.td.0.a.span.title [copy as] titulo.
As I said you could do it your way, why doesn't it work? mainly because reading your expression pipes interprets some of it, which does not appear in your regex formula when it is applied hence troubles... or at least that's the conclusion I've reached and why I'm careful and don't try to do my regex in one big formula.