Mic pre-amp vs. Line matching transformer (for keyboard mic in)

[PianoTone]

So I love the mic in feature on my Yamaha PSR-EW425 and my new Yamaha CK61; they both have adjustable volume (max'd) and gain knobs (max'd) and they're usable but kinda just barely. Started looking for battery operated pre-amps and came across this video on a "line matching transformer" from Shure that seems to boost mic volume in this video. I'm not a techy hardware type; anyone got any thoughts on whether this would bump up my gain enough (at all)?

https://www.amazon.ca/Shure-A85F-Transformer-Female-4-Inch/dp/B0006NMUHW?th=1

 

[PianoTone]

Ok update! I am still curious what exactly the line matching transformer does, but I found a setting in my CK61 - it defaults to line level input (you can use guitars or other keyboards etc through these ports); you can switch it to mic instead of line and the gain is awesome.