I got my Helix LT a few days ago, so I'm sure this is a very nooby question....
But I have noticed when making my own presets, occasionally I will go to add another effects to the signal path and the majority of options will be unavailable (kinda greyed out). From memory the volume option is usually selectable, and even some distortions (but not all).
These aren't crazy paths either, there might be 4 or 5 blocks in the chain but I try to add another and it seems to have hit some kind of limit.
Any ideas? From the presets it's obvious that a lot more effects and amps can be added so I'm definitely doing something wrong!