Will I benifit form a external phono stage

IMO, you will get an improvement. The two phono stages that you mention are very good ones for the money. Nothing really wrong with your HO Benz, but, in general, LO will be a little more detailed due to lighter moving parts. Being able to "load" the cartridge properly with your new phono stage will help also. Regarding the mixing of tube gear and SS gear, many people do that to get some of what they like about tube sound combined with what they like about SS. Particularly in the phono stage, since that is very early in the signal chain, the tubes will provide a very nice smooth signal for the SS stuff to work with. I expect that you will like it. You might like it enough to change the rest of your gear to tubes.

Yes, Zaikesman, you are correct, finding good low noise and low microphony tubes for something as early in the signal chain as a phono preamp is somewhat of a pain. I like to use NOS tubes which is even harder and more expensive than the new-made types. Overall, though I feel it is worth it.
I also agree with others above that upgrading the TT would be of great benefit, more so than the phono stage. I didn't mean to ignore that point, but concentrated on what seemed to be his main point of interest.