How to reduce transformer secondary voltage?
After the thought provoking comments above, I decided to operate on the transformer for some flexibility. I carefully removed the 6V and Common connections from the binding posts, and isolated them. So now I have four 6V windings. The transformer capability is shown below (Amps DC on X axis, VDC (regulated) on Y axis, for the 4 windings if connected in series).



I can potentially get about 6V @ 1.5A from each winding, or 16V @ 1.5A from two windings in series. Two windings in parallel now give 6V @ 3A. And, two windings in series times 2 gives 16V @ 3A. With a XL6009 boost converter, I might be able to get 24V @ 2A from this. So, I guess that solves the problem. Multiple windings are better than a continuous one.

I'm planning to do something like this https://www.youtube.com/watch?v=-04CQ0Mug1o&amp;t=865s (HP E3610A), but for 2 channels instead of one. Each channel with a switch to toggle between 6V @ 3A and 16V @ 1.5A. There will be 2 of those. So those can again be paralleled (6V @ 6A or 16V @ 3A) or put in series (12V @ 3A or 32V @ 1.5A). So that's a lot of possibilities. The two 6V windings of each channel can be connected like this, before it goes to the linear regulator for that channel:



There is a toggle switch to connect/disconnect common terminals (see long wire near wire marked "common"). There will be no short circuit due to the bridge. I will lose a few volts, but hopefully the amps and flexibility will make up for it.