こんにちは (Konnichiwa) toru e and イ リ ニ,
Thank you for your question!
This is a tricky one!
As you've both realised, the first に は (ni wa) means "as for," so when we use it with the noun わたし (watashi), we can say "as for me." However, the second に は (ni wa) actually means something a little different.
The に (ni) in おもしろそう に は みえません (omoshirosō ni wa miemasen) is actually part of the grammar construction に みえます (ni miemasu). When we add に みえます (ni miemasu) to a な (na) adjective, we can say that something "looks like" or "appears as if."
そう (Sō) is a な (na) adjective, so when we add に みえます (ni miemasu) after it, we can say "it looks interesting."
おもしろそう に みえます。 (Omoshirosō ni miemasu.) "(It) looks interesting."
Or, in the case of the example above, we can make みえます into the negative: みえません (miemasen) and says "it doesn't look interesting":
おもしろそう に みえません。 (Omoshirosō ni miemasen.) "(It) doesn't look interesting."
So now that you know what the に (ni) is for, let's look at why we use は (wa)!
When we add a は (wa) after the に (ni) in this sentence, we can imply contrast. In this example, it shows contrast been looking "interesting" and looking like something else: like boring or difficult.
Basically what it's saying is something like this:
おもしろそう に みえません。 つまらなく みえます。 (Omoshirosō ni miemasen. Tsumaranaku miemasu.) "(It) doesn't look interesting. (It) looks boring."
We can imply all of this just by using は (wa):
わたし に は そんな に おもしろそう に は みえません。
(Watashi ni wa sonna ni omoshirosō ni wa miemasen.)
"As for me, (it) doesn't look that interesting (it looks boring)."
If you want to read a little more about how to use は (wa) to show contrast, you can check the section on は (wa) in this brand new lesson:
https://members.rocketlanguages.com/members/japanese/lessons/5045/2-7-Joining-Words
イ リ ニ, to make your example sentence correct, you would need to add a に (ni) before みえます (miemasu). The rest is perfect!
toru e, unfortunately, わたし に は そんなに おもしろそう ほん (本)/こと
を みえません would be grammatically incorrect. Instead, you should say this:
わたし に は そんなに おもしろそう な ほん に みえません。 (Watashi ni wa sonnani omoshirosō na hon ni miemasen.) "(It) doesn't look like an interesting book."
Since そう (sō) is a な (na) adjective, we need to add a な (na) to modify the word "book."
Also, it's true that normally you would use を (o) with みえません (miemasen); however, since we're using the grammar structure に みえます (ni miemasu) "looks like," we need to use a に (ni) here instead.
I hope this helped! Please let me know if you have any other questions!
べんきょう を がんばって ください! (Benkyō o ganbatte kudasai!)