The power section is essentially the same, the 2555x has much more responsive tone shaping and more gain. My understanding is the diodes are not in play on the clean channel with the rhythm clip not engaged. Obviously it has more gain than a 2203 and uses diodes on od channel.
For a band that has one amazing and one decent guitar player, night ranger sure was a let-down.
Gillis was a total monster with Ozzy, then he had to chop off his balls to make cash on the radio playing sappy crap.
Damn shame.
Just my 2 cents.