Differences between Line Magnetic 518 and the 219

I own a 219ia and I bought it after many auditions comparing it to the 518ia and also the 508ia.
I bought the 219 mainly because it was a very good deal (excellent value pre-owned).
Regarding the sound, as mentioned before it's not that different from the others if you run it as integrated. It has more weight, a more "dense" and solid sound. Maybe more layers and better image, but that will depend on the speakers as well.
But running as a pure power amplifier, everything changes! - given the fact that it is fed by a good preamp.
I am running mine as integrated (negotiating a preamp right now) but I heard it playing connected to a Rogue, a Melody and also a passive preamplifier. The passive didn't convince me - it subtracted much of the musicality and sweetness, because replaced the pre amplification stage with...nothing. But with the Rogue and especially the Melody (don't remember the models), the 219 was superb! A true musical beast!

I've owned both,..  currently still have the 219,... I originally sold the 518 because I was very curious about an Ayon integrated with it's discreet vol. control.  While I had the 518  I acquired a Wytech pre (Jade 2.1)  and it convinced me of the better sonics to be had with a discreet based vol control.  I sold the 518 and regretted it.  While the Ayon (Spirit III/KT150) was an awesome amp,  with the Zu's, it lacked the emotional portrayal of music that the 518 was able to deliver.  I should note that the Ayon drove my Meadowlark Osprey's much better and was the clear winner over the 518 though.  Anyway,  I digress.  I sold the Ayon and was able to purchase a 219.  The 219 if running in integrated mode is very similar in sound to the 518.  Maybe a little bit more weight and body to the sound but close.  Nothing really to get overly excited about.  I would say that the degree of difference you hear will most likely be very speaker dependent.  However,   run the 219 in amp mode and hold on.  Then the difference really does become night and day.  The gain in clarity and realism jumps by a noticeable margin.  I believe some of this probably has to do with omitting the 'AX7' gain stage and dumping the input directly to the 310's.   In the 518,  the 'amp' input only bypasses the vol. pot but still runs though the 'AX7's'.   All in all,  unless you have the ability to run direct into the 219 I would save the $$ and spend it on more music or other gear.  Hope this helps a little!

Good suggestion,I've read this review before and found it well written and insightful.

If you haven't yet read it, Steve Huff has an extremely detailed description of his experiences with the 219 and compared it to the 518, which he also had in his house.

http://www.stevehuffphoto.com/line-magnetic-219ia-integrated-tube-amp-review-300b-and-845-tube-magic/