Welcome to the Forum, Bob. Don't give-up on H.A. Gold Sound just yet! It is true that in this day and age more realistic sounds are available ... provided you have the resources.
Many instruments can be made to sound more realistic by the application of attack/decay, tremolo and grace-note effects.
If you download* the attached score extract, then view the harmonica part in Scroll Mode (Cntrl-G), you will see the greyed-out attack/decay marks. (Grey, because I selected them to be non-printable, therefore not visible in Page Mode).
If you double-click on one of the grey <> symbols, then on Edit Effects, you will see the parameters used. In particular, for longer harmonica notes the decay represents the player's natural falling-off of breath pressure. If any note requires emphasis, then you can apply a marcato (>) effect or change its velocity (General note option: double-click on a note). Shorten a note's Pressure Time for a staccato effect.
It does require a bit of effort (trial-and-error) but once you have found a suitable improvement for a particular note length, H.A. will apply that setting to each future application of that effect. You can also copy-paste a previous note with effect* then change its pitch as required.
* Using the Firefox browser, double-click doesn't open a file any longer; right-click and Save-As.
* Notes can be copied with or without their effects by selecting/de-selecting the appropriate icon on the Action Tools palette.
H.A. (2009)+Gold Sound+ Virtual Singer, Windows XP3, Firefox. Anglophone
Interesting sound Tony. I think the the dynamic markings are a strong point of HA. I use various high quality external sounds with HA but I still find myself adjusting the sound with these effects. Luckily the note shaping is sent via midi as well. They can affect quality sound fonts and many VST's correctly.
I found it easiest to use scripts to make some preset volume shapes. eg. staccato falling to various lower volumes ( rather than to just zero) or volumes that rise, or rise and fall, to various levels. Following one of your suggestions, (I think it was you?) I stored the scripts in a palette which sits conveniently visible. The scripts change whatever notes or staves you select. And take account of whether the pressure length has been altered . I will dig out the basic script ( but I had better check first for any of my usual errors!) and put it here so it can be modified by anyone interested.