I would take the Modulus 3A first. I own a 3A and the 3B preamp so I am biased. Second choice would be the Prima Luna. I have heard a lot of their equipment and like what I hear. Last would be the Sonic Frontier as the line is no longer made. Even though the Parts Connection can service it, I personally wouldn't touch it. You should be able to pick up a nice 3A for a grand or less and it has a great phono section too.
Prima Luna or sonic frontiers or audible illusions
I have an audible illusions 2d. It has served me well for many years. But, it seems I have the upgrade bug of late. I am looking to increase the imaging if possible of my system and am curious if upgrading to the modulus 3a would be a significant improvement. Or, would I be better served with a sonic frontiers sfl1 or line 1/2? Lastly I have to admit that the prima Luna prologue is appealing bc of the exposed tubes. Not sure on the sound though...any advice? Any other choices that have the tubes on display?