I would choose Grooten because you have already read a positional chess book by Silman.
I also started with reading the Amateurs Mind and then bought HTRC only to find that it was essentially a rehash of Amateurs mind with a few other things added (like endgame opposition). But since it was essentially the same ideas by the same author (but with different examples) it was virtually like reading the same book again and I lost interest.
So Grooten would be delivering positional concepts but in his own style and with his own examples and being different to what you are familiar with might help. But always get the book you want most. If you get a book but really wanted another one then you will lose interest in reading it.
If you want to focus on positional chess though, I would recommend a positional problem solving book instead (as you already have solid positional groundwork from Amateurs mind) and if you want to keep to Silman then look into his "Reassess your chess workbook" instead.
I've read Amateurs Mind by Silman and Simple Chess by Stean.. What's the best book of those two to read next? Chess Strategy for Club Players or HTRYC? I understand both are good but please tell me your experience with either of them.