Not an expect here, but do know a little. You mentioned you have hydraulic steering. My question is where does the hydraulic power come from, normally hydraulic power comes from the main motors, but could come from an electric pump as well. But if it comes from main motors, you won't have power steering unless they are running. Now manually steering a power system without the power assistance is possable but very tiring on the arms. I think we have all driving a car with ps that is not running and can be a work out.

I would think your hydraulic steering would be one of the main reason they are saying use an electric power unit instead of just a tie bar.