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? 

Hi there!
I owned two of these in a home theater set up. I agree with your description, but I want to encourage you to absolutely leave it alone. This is a gateway amp for many people. Yes, it’s good, but it’s good in a way that makes you look for even better, evidenced by your desire to mod them already.

Leave them alone and trade up when you have to so you can preserve the resale value.

As for the bias, I did some power measurements on them at idle. They already run hotter than spec, and I suspect they are already biased warm, do not adjust.

The only mods I might encourage you to try are to build your own IC and power cables. The amp’s XLR inputs are convenience, not real so don’t force yourself to use balanced IC’s.
I’d recommend using DH Labs shielded power cables, and pure silver IC cables with KLH plugs. See what you learn.
Of course, if you are just getting into high end audio, I always encourage you to invest in room acoustics as early as possible.
Thanks Eric,

Just for my own curiosity what would be an amp that you would see as a clear upgrade to the A21 not priced in the stratosphere. Similar power specs let's say 6k or under new price. 
The latest version is the A21+, maybe Parasound can tell you what's different and maybe they have an upgrade program. 
Hi OP :

Luxman and Ayre are brands you should listen to which you can find in that price range used.