Hi Classy,
NPS (North Penn S Gaugers) use both Hi-Rail and Scale on our modular layout (American Models Track). Finding a particular engine in S Gauge (hi-rail) may be difficult, finding it in S Scale may be very difficult. American Models does offer a very limited amount of engines with scale wheels and couplers.
Standard AF/Flyonel and old S Helper can be converted. However, S gauge engines are very sensitive to track irregularities - things that wouldn't bother S gauge will derail S Scale. Also you can't use more then 1% grade on elevated track - granted this is with brass engines - don't know if others are similarly affected.
Yes the Legacy works with a variety of command systems; TMCC and DCC as well as standard transformer control.
One of our members is doing a huge S Scale layout that is absolutely beautiful and prototypical DCC. Most of his engines are brass, but all converted to DCC.
Hope it helps.
