i had the vk-30 before moving up the the 30se. i never tried the line 2. the vk-30 is not at all "dark or airless" nor (until now) have i heard it described as such. in fact, i'd say it can even be a little bright when poorly matched with cables and front end. it has good detail and staging with fairly neutral timbre.
the main deviation from neutral that is widely reported (i noticed it too) is a slight chestiness in the midrange that becomes prominent on certain vocals. the bass got a little weak and/or loose sometimes as well. however, note that many of these "problems" can reportedly be corrected with tube rolling, although i never tried it in mine. oh yeah, the interface of the 30 is great and (i expect) better than that of the line 2 as well as most preamps out there.
to me, the best aspect of the vk-30 is that it can be upgraded to a 30se, which turns a very good preamp into a great preamp. everything improves in the 30se: better detail, more solid and 3-dim imaging, more "air", tighter and stronger bass, better treble extension, etc...all improved to a HUGE degree over the stock 30. when the AC current (or whatever) has been perfect, the 30se in my system has produced that amazing and rare sense of 3-d realism on certain vocals and instruments that just grabs your attention. this is an incredible experience when you hear it (which is not often at all).
the 30 is a very good preamp. i would not hesitate to get one especially if you're willing to experiment with tubes.
