Krell KSA200S with tube preamplifier

I want to upgrade and replace my Krell KRC2 preamplifier.
I want to go to tubes.
Speakers are Sonus faber Electa Amator II.
I need preamplifier with balanced input and output.
Some options are:
Sonic Frontiers Line 2 or Line 2 SE
Bat VK30SE or 31SE
Other suggest would be accept.
I would tend to be careful with a BAT pre and a big solid state amp, I have read of some issues with BAT pre's passing DC and causing damage to big SS amps. This is in no way a condemnation of BAT preamps I think they have excellent sound quality and are very reliable, but this is a very real issue and should be considered. A search under "dc offset" here and at would show you the appropriate discussions. Good luck!
Balanced...Sonic Frontiers and Audio Research are both good matches with your amp. Many other tube pre's would also sound fantastic but your need for balanced will keep your list somewhat small.

I use a single-ended tube pre with my Ksa-250 and am very happy with this blend of SS and tube sound in my system.