It's fairly easy to make soft, acidic water hard and alkaline. You just add KHCO3 or NaHCO3, Ca, Mg, maybe other minerals/trace elements. This is also how you would build up ro/di water.
But it's very difficult to make hard, alkaline water soft and acidic. You have to erode the cabonate/bicarbonate buffer with an acid like pH down. As a result, the CO2 level in the water rises temporarily and pH drops. The more the buffer is eroded; the more co2 released; the greater the pH swing over the same time-frame. Trust me, it's not something you want to do.
You also don't need to do it. There's nothing wrong with a pH of 7.8. Your KH might be 5-6º which is very good for SA cichlids. A pH 8.8 is hard, alkaline water.