...because you mentioned wanting a touch of warmth. The SFL-2 will be (slightly) warmer, and in my experience a bit more 'organic' sounding than the Line 2, which is more neutral, although nowhere near as good as a fully modded Line 3 IMO, which is the most neutral of all, yet with proper modifications, extremely full-bodied, and with a jet-black background, quieter, and yielding much deeper bass than a Line 2.
Re: the SFL-2, I find the overbuilt full outboard power supply contributes to the excellent detail retrieval as well. This is why I recommended it as a great 'balance' to suit your needs, plus it is fully balanced if you have a balanced source and/or amplifier.
I have a modified SFL-2 and a modified SF Line 3 as well, and they are both superb, but for different reasons, one using greater negative feedback than the other, giving a slightly different sonic signature. I have owned and heard many preamps, and have settled on Sonic Frontiers (but only the highly modified versions, done by an Electrical Engineer friend of mine who knows the SF gear inside and out).