Battery emulator based on an array of buck converters for BMS testing
Nominating a specific BMS would be better - they MAY vary in action. 

Presumably you are "top balancing". As shown each buck converter needs to provide progressively higher voltage and power -
eg if BMS conducts at say 3.6V and up to 1A - 1st buck supplies up to 3.6w,
2nd 7.2W ...
and 16th at 16*3.6 = 57.6V supplies 57.6W.   

For a 206 Ah cell the balance currents may be some amps and your top buck handles hundreds of watts. 

IF you can use isolated bucks each handles only Vcell_max x I balance
= much less watts.
You could use 16 x isolated psus. 

Consider microwave oven transformer with HV secondary removed, magnetic shunt removed and 16 low voltage secondaries. Also add about 10% more turns to primary as core tends to run well into saturation usually.
Separate psus may be easier. 

Also consider a string or 16 resistor pairs in series with a switch allowing one // R to be removed. If usually dropping say 3.55V each. opening the switch on one R pair will raise the voltage on that resistor.

Consider using 16 series resistors and add an isolate psu across any one R to increases its voltage. Wind up main voltage until all R's are JUST at BMS start point and then add extra I to one R. All extra I should exit via BMS