You could exceed voltage limits if the load impedance were too high, or you could exceed current limits if the load were too small. In many cases, you have a pretty wide working range, and in that case the load impedance can be set as needed, within reason, perhaps anything above a few hundred ohms. But in some cases, the source limits can be reached with values much narrower in range, maybe 20k on the low end hits a current limit and 250k on the high reaches a breakdown voltage. The only way you can know is to study the particulars of the output and input circuits, especially the active devices. Capacitors have a breakdown voltage, so while that isn't usually an issue at preamp levels, it could be in some tube circuits.