To be fair, those are three very different keyboards. I'm not familiar with Hohner, but that model looks like something in the PSR-E200-300 range. The PSR-540 was a mid-range model, something between an E400 series and an SX600, as the model number would suggest. And of course, the Tyros was high-end. I'm not sure what was high-end in 1993, but I know Yamaha had the PSR-500 and 510 mid-line models back then (predecessors to the 540), as well as higher end models. And when the PSR-540 came out around 1999, Yamaha had high-end models like the PSR-8000 and 9000, which were more comparable to the Tyros than the 540.