I dont have Old Lady - but I highly doubt that you would ever need more than two ports for a piano. If I understand you correctly you only have two ports - meaning you have 32 midi channels. This allows for 32 articualtions which I dont think any piano would require? It would only be a problem if you want more instruments than just a piano, in which case you might run out of channels fast
I have the Old Lady and Giga 160, where it indeed sounds wonderful with 3 MIDI ports. The Giga MIDI ports are not used for more channels, but instead are "chained" to allow more layers (release, pedal up/down, etc.) to play concurrently. This is a unique feature (quirk?) of Giga 2.x. Giga 3 has removed some of the limitations that made use of such "chained" MIDI ports necessary in Giga 2. You should be able to play the Old Lady with less ports by giving up one of the layers, but of course the sound will suffer for it.
I'm not sure you can even upgrade Giga (2.x) 96 to 160 anymore. You might consider upgrading to Giga 3, and the 24-bit Giga 3 version of the Old Lady while you're at it.