I might SBR the PS90 later. I have many more guns. These were just the Bullpups and HKs. They are what I'm into right now. I'm looking to buy more HK pistols!
Can't blame you for that. But the addiction runs high on this board. I might be the first to tell you, but won't be the last, that you need to add some good HK rifles to that collection. Whether quality clones or genuine HKs, the roller lock guns are a blast. A G36 conversion, since you already mentioned that you like it, is a good way to get started. And there are a couple of guys on here that do a great job on them. Post in the clone section or contract Chopstix Kid directly. They've made some really beautiful versions of G36 or G36K.
If you want to get into something a bit cheaper, there is the Vector V93. The Century C93 is even cheaper but quality is lacking in a lot of them. The V93 should be about $1100-$1300. Or you could pick up a nice PTR-91 GI from CDNN for around $1000.
Those pistols would look even better with a couple of HK type rifles with them.
There is no cure for the addiction. Only treatment.
ETA: Here is part of my HK collection. I've added a number of things since this photo. The extra furniture around the pistols is for when I have the auto sear installed. So there's no problem with constructive intent. I just put the stuff in the photo to give a better idea of what I had for each gun. Click on the photo to see a bigger image with more detail.