I think it's mostly just a matter of degree, within the natural variability of the type range. Some IxTPs will interact within their aux as well as accept information through it -- it's a two-way pipeline. Whereas some others just take in data through it but express themselves more via their primary, so the aux is kind of "transparent" within the process.
I guess my question here is, when you mention extraverting, are you talking about IRL face to face, or do you mean extraverting via writing? (I think it's much easier for IxTPs to express Ti in writing.)