If I had any component that was "dead in the midrange" it would not be in my system very long. Boy, if you don't have the midrange right, then it will be very easy to find an amp that does better. I heard a friend's modified Dynaco many, many years ago and was very impressed with it, but couldn't comment beyond that. Have you tried rolling the tubes with various different brands? Could you have some bad tubes in there that are holding it back?
As far as a replacement, as Tvad points out, you might want to post the speakers you are using in order to get more informed input on the subject. Are you intending on keeping the other Dynaco components? The price of the "most realism possible" can be very high indeed. Also, what you find to be "realistic" may be different from what another person finds that way. You should probably also consider stating a budget, or you will get suggestions from a few hundred dollars to tens of thousands of dollars.
Marco
As far as a replacement, as Tvad points out, you might want to post the speakers you are using in order to get more informed input on the subject. Are you intending on keeping the other Dynaco components? The price of the "most realism possible" can be very high indeed. Also, what you find to be "realistic" may be different from what another person finds that way. You should probably also consider stating a budget, or you will get suggestions from a few hundred dollars to tens of thousands of dollars.
Marco