The lack of cut-off is the most noticeable, which is probably why someone once described the puffs as sounding no better than a peice of cardboard being flipped by the spokes of a bicycle wheel.
A starting sequence is roughly as follows : Wind reverser into full forward gear, open drain cocks to dispense with condenced steam, blow whistle to warn of impending movement, open regulator to fill steam passages then slam shut. Reopen and tickle until loco begins to move, then open fully. Loud exhaust beat as loco begins to move and takes up weight of the train, draincocks are partially shut then reverser is wound back a touch to use expansive nature of superheated steam resulting in quieter exhaust. As winding back reverser continues the exhaust gets quieter. A pal of mine has set his "sound" so that the loco automatically increases its 'bark' when it senses an incline. I'm not sure if it automatically goes into clanking rods mode downhill or if he sets this by pressing a button on the hand control.
From what he has achieved, I think a decent steam sound is possible with todays equipment, but it must depend on where the sound chips are obtained as well as the size of the speaker. His locos are American narrow gauge 7mm scale running on ¾" gauge track.