How much would I benefit from an amp upgrade?

I did a ton of upgrades this year and in my experience the amp upgrade makes the smallest difference and the room treatments make by far the biggest.

Get the current Krell 300 series integrated; they list at $2500 and appear on here regularly for around $1700. Will sound MUCH better than the kind of amps you mention; not all watts are created equal. The 203 deserve a better quality amp; but don't forget the room treatments either. Just to check I took most of mine down last week and the sound was much worse.

My experience is in going from a BAT power amp for two channel to a NAD 763 paired with a M15 prepro for video. I kind of got out of Vinyl for a while but recently replaced the M15 with a NAD T175HD in order to be able to decode lossless codecs and 96k. The surprise for me was I think the two channel sound (which I thought would get worse) is actually better, perhaps due to the ability to use Audussy in a difficult room. I think I am getting the best sound ever from my vinyl now and I have been in this room for 20+ years and at one time had Appogees and a Krell.

Long story short, while I am probably giving up a bit to the BAT I am very happy with the sound. While not directly related to your equipment the point is that some relatively inexpensive power amps stack up quite well against some well regarded expensive equipment. On the other hand this rig is head and shoulders above a Yamaha receiver I used for a while when I first went into theater.

i agree regarding the krell s300i. can be found dirt cheap considering the power and HT features. had one for a while and enjoyed it. give one a try if you can. easy to flip used units if things don't work out.

I think you'd benefit a lot with a better amp. Right now there are a couple of new and demo Theta Intrepid 5 channel amps on Audiogon going for around $1,400. IMO, that's a no-brainer.