I have created two groups, each group consists of three parallel pins. Each
group of pins drives one side of an ultrasound piezo transducer. This works
great. The signal even looks good on my scope despite the high capacitance
of the transducer. AFAICS the current supplied by the parallelled pins is
evenly spread among them, as was expected. Because I only had two
multimeters (one digital, one analog) there may be some inaccuracy in my
measurements, but it can't be too much.

Thanks for everyone who helped!

Marcel

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