Every single one of those Consumer-grade step/up/down transformers are a piece of shi**. Tried that route several years ago and despite only pulling 1,400w each from 2 of those - both rated for '3kW - they were literally crispy fried in less than a month. There is a reason they are so cheap - very thin wire in the primary and secondaries along with simple paper insulation.
If you absolutely need to use a transformer, get a REAL commercial/industrial rated one from Grainger, McMaster or AutomationDirect.com. They are absolutely bullet-proof.
and this is 370
https://www.evga.com/products/product.aspx?pn=120-G2-1600-X1
it will run 1 s-9. if he did what I said 600 + say 200 to the electrician for the 220/240 line
total 800 and he can run 4 s-9s vs 4x 370 = 1480 to run 4 s-9s with 120 volt outlets and every out let must be the only thing on the circuit.
Point is - is ALWAYS better to just bite the bullet and get proper 220V power. Got an unused electric dryer outlet in the laundry room?