Not to belittle your purchase, but i can believe that there might not be a drastic difference between your old "Dyna" and the Acurus. Many of the old Dynaco products were "overachievers" in terms of price and age. If the Dyna was a current product, it is quite possible that it would cost at least as much or more than the Acurus that you've mentioned.
With that in mind, i've noticed that a piece that is WAY better than the old piece can be "held down" or limited in performance by the other components in the system if they are not up to snuff. In other words, the old adage "only as strong as the weakest link" still applies. As such, buying new gear to replace old gear might not seem like a step forward for a few reasons. Any / all of these MIGHT apply to your system.
(1) Synergy. The "old" combination may have actually worked quite well together. Just because it might not be "the latest & greatest" does not mean that it isn't capable of quite respectable performance.
(2) The new component does not compliment what you already have. In effect, it MIGHT be a better component but just isn't "right" for that specific system. As hard as it might be for some to swallow, the new component seems like a step backward.
(3) You are used to hearing things a certain way. If the new component sounds "different" this can be percieved as "better" or "worse" depending on one's mood or personal tastes.
(4) It is possible that there are little to no differences between specific components. As such, this sometimes takes time to become familiar with them or notice their strengths and weaknesses.
(5) The component that you replaced was NOT the "bottleneck" in the system. As such, ANY component that you put into the system may run into a "brick wall", i.e. the component that IS limiting the sonic potential of the entire system. Until that weak link is removed, everything is limited to a "sound" or level of detail. This can result in all components sounding the same or changes making a minimal difference. You've heard of systems "not having enough resolution to tell the differences between components" ??? That's why some changes seem more like a step sideways rather than a step forward.
These are but a few things that i've encountered along the way. I'm sure that others can add to this list with a few other experiences of their own. Sean