I liked Sumo amps a great deal in the day. The problem wiht all that vintage gear is that it may be seriously outclassed (or not) today and the power supply components are aging and will need significant maintenance.
The usual neutral, affordable amplifier standby’s are Parasound Halo amps. I’d listen to those and if they don’t sound much better than what you have use your own judgment about what to keep, but plan on recapping now rather than later. Otherwise sell everything and get the smaller 100W/Ch Halo. I forget if it’s the A21 or A23.
Remember that amps are bad when the caps go. They can have cascading failures that leave you with lumps of metal you can't get fixed, so whichever amp you are keeping, at this age they need to be recapped.