Hi unhappyhacker,
"my 88 key Yamaha thuds a bit throughout the house"
I could be wrong but maybe the problem isn't your keyboard. I'm thinking that somewhere, there is a person complaining about the "thudding".
Is there a baby whose sleep your disturbing? Is your keyboard on a wooden floor over someone's bedroom (perhaps the downstairs neighbor)? Is a sibling trying to study or are your parents just trying to watch some T.V.? Maybe your wife gets up very early for work and you practice late at night?
I don't know. I haven't a clue. So, if something along these lines is the case then...
It might be a simple fix to eliminate the thudding (disturbance to others). Oh, it will still thud but hopefully, only in your room! Wouldn't that be wonderful? You could use your 88 key Yamaha!
I would try an inexpensive carpet on the floor if there isn't one. Bare floors can really echo throughout a house! Can you rearrange your furniture in your room? I mean move the keyboard to a different wall further away from the "person" your disturbing. Is there a big crack at the bottom of your door? Place a bathroom towel there when practicing and plug the leak!
Perhaps some heavy drapes on the window? Hanging a quilt on the offending wall can act as a sound barrier. These sound barriers are very common on highways and effectively work to reduce the road noise to the local residences.
How about just practicing your scales/arps/broken chords at a different time when they're not home?
P.S. I would say headphones but that wouldn't eliminate the thudding, would it? Finally, do they complain about the thudding ALL the time even when your playing pieces? Or is it just when you practice scales/arps/broken chords?
I hope I have been helpful, Joe.
P.P.S. You could just practice your scales/arps/broken chords hands separately, "thuds free", on the controller when they're around and hands together "thudding away" on the Yamaha when they're not.
Topic: How many keys for practice