Sunfire classic tube pre amp, Difference between the Signature 97’ and non Sig. 01’model

I’ve been looking far and wide to find technical info on what mods were done on from the  original  year model  97’ Sunfire Signature classic tube pre amp  to the Sunfire “ non” signature  year 01’ classic tube pre amp , which I now own both ,  and  continuing on the later models of the Sunfire Classic tube preamps. Looking  on what Bob had done to them in bettering the sound quality to the final productions.  My 97’ Sunfire Signature classic tube preamp  has a phono Board, and the  01’ Sunfire Classic tube pre amp “ non” signature  has a remote board . I was going to combined the phono board and Remote board to one Amp, But I’m not really sure which of the two is overall the better amp. I’ve read that he improved the power supply and changes in the quality of the electronics , Caps, added resistors, etc. as the years went on, But I’ve been unable to really find out what actually and technically was done to them through out the years to the final productions, But , What I found in the reading and researching  that there were improvements along the way, and read that in the final years of production the Sunfire “Signature “ classic tube pre amp models combined the better electronics and power supply and all  additional improvements, But I don’t believe he made another Sunfire Signature classic tube preamp after the original year of 97’ , at least I haven’t  seen one that was made after 97’ , which is really confusing . I love the look and sound of the Sunfire pre amp, and would like to keep it in the system and would really appreciate any help and information on how to Lower the noise level and better the sound quality as I’ve read was done in the latter years. I  greatly appreciate any info and help on this, I’ve found as much as I can so far. 
There is very little information out there on sunfire in general , So I’ve decided to reach out for some help.
Thanks