The basic rules of the Pronto Hex string are pretty simple. The position I marked in red in the first example gives half the length of the "one time" part and the position I marked in blue gives half the length of the repeat part.

If you concatenate multiple signals, only the last signal can have its repeat part represented in the Pronto Hex repeat part. But the actual device can't know or care whether the repeat part of the signal is represented in the repeat part of the Pronto hex. It just knows how many times the repeat part of the signal gets sent. You already have seen how to include some number of copies of the repeat part of the signal in the one time part of the Pronto Hex.

So after some number of copies of the repeat part of the first signal, the one time part of the Pronto Hex could continue with the one time part of the next signal, and so on.

I don't understand why you couldn't get the MX to send more copies of the repeat part to get more than 2 db. Maybe you did it wrong (making the MX editor see a repeat pattern that it removed) or maybe the MX editor enforces some limit on either the string size or the total duration of the one time part of a signal it imports from Pronto Hex. I don't know its limits.

In Pronto Hex, you should be able to concatenate signals as you requested. But it is hard to imagine any version of limits in the MX editor that wouldn't be a more severe limit on concatenating signals than on adding a few more signal repeat parts to the Pronto Hex one time part.

So in theory you could do it. But my guess is whatever prevented getting over 2 db the direct way will also prevent getting over 2 db this way.