Parasound a21 upgrades

Bought a lightly used 2 year old Parasound A21 some days ago. It has exceeded my expectations for sure. Right up my alley warm mids and non aggressive highs but also dynamic and tight with lots of headroom. 
Are there any mods that are reasonable to do to these amps? Fuses etc. Can the bias be safely increased to add more class a watts? 
Also have there been any changes over the years? So is a 2 year old A21 the same as a 15 year old one? 

Oh my yes! Could easily be10k and worth every penny.
For a single box a JC5 for sure. Mono’s JC1s. I agree with Eric, PC’s are a great add Parasound gear seems to like Shunyata power. Not much else really. You are getting into the price realm when there are so many great options, it’s really tough to nail them down. The A21 is an excellent amp.
@erik_squires, if memory of your prior posts serves, I thought you have previously owned the Parasound A23, which sells for about half the price and has about half the watts of the A21 the OP has purchased.

Where the A23 could be considered Parasound’s entry into their higher end line, not so the A21. Whether you care for the warm sonic voicing of the amp is personal preference.  Note that the A21 remained unchanged for 17 years before the upgrades performed in 2020 resulting in the name change to A21+.
what preamp are you using?
a great way to upgrade your amplifier is to upgrade your preamplifier.  
balanced cables could benefit too depending on your preamp.  
I'm running RME ADI-2 dac directly into the amp. Also tried with my upgraded Joida Pre and prefer direct for sure. I only do digital so I see no need for a preamp. 
I tried balanced and unbalanced and heard no difference which makes sense since I believe the A21 is not truly balanced.