「〜そうにない」 unfamiliar usage of そう


I'm playing a video game in Japanese, and one of the characters said

> 僕にもわかり **そうにない** 。

I understand that (verb stem)そう means "it seems" or "it appears", but I've
never seen (verb stem)そう used with the に particle.

My guess is that the sentence means something like:

> I don't seem to know either.

Am I translating it correctly? What is the meaning of this construction?




Your translation is correct.  
「そう」is for positive sentence, 「そうに」is for negative sentence.  
「そう」/「そうに」also have some meaning of "in the future".

I also understand.

> 僕にもわかります  
>  僕にもわかる

I understand... maybe.

> 僕にもわかりそうです  
>  僕にもわかりそう  
>

I don't understand.

> 僕にはわかりません  
>  僕にはわからない

I don't understand, ether.

> 僕にもわかりません  
>  僕にもわからない

It's hard to understand. Ask someone else.  
「そうもない」is much harder to achieve the goal than 「そうにない」.

> 僕にはわかりそうもありません  
>  僕にはわかりそうもない

I don't understand ether.  
Nearly same as 「わからない」 but 「わかりそうにない」is a little bit soft.  

> 僕にもわかりそうにない  
>

"(I'll try but..) it seems too dificult for me to understand"  
「わからなそうです」is more softer expression  

> 僕にもわからなそうです  
>

