What Audio Research preamp would be an upgrade to my LS2B

I am thinking of upgrading from my Audio Research LS2B to another Audio Research preamp. It would have to be substantially better so if any one has any advice it would be appreciated. My other equipment 
is a Mark Levinson 532H Amp and a Audio Research PH3 with a VPI Turntable.
hollytone22---Wait a year and buy the LS28 Mk.2 ;-). It will no doubt "make the LS28 sound broken". Or get an Atma-Sphere Mp3 or Ear-Yoshino 868. Both are available as line stage only or as line & phono stage, so you can ditch the PH3, a dated design.
Thanks for the insight on some of the options that you mentioned.
I will explore my options and see what works best for me.

i had a LS2B as one of my first serious preamps. The upgrade to a ARC SP 16 was a huge jump. The LS2B was a bit dark and rolled off compared to the SP16. Honestly, the LS2B is a dated design with its single bottle that any upgrade will yield sonic benefits, IMHO
Guy's I took your input and upgraded to a LS25Mkll and yes it is a tremendous difference. Lostbears I went with your suggestion and it
was dead on. All the rest were great also and I appreciate the advice.
Time to go and listen!!!