Thanks for all the follow up!
In Aventa 3.27 there are 977 & 577 variants (respectively 8 & 6 for each) as in LiNX, LiNX2, Alera, Verso, UP Smart & UP models & some with 'T' suffixes e.g. AL977 & ALT977, but not the particular ones sought after! There is for example a UPS977 DLW and a UP967 DW but this latter is a smaller MBTE model with #312 battery rather than the BTE UP977 DW at hand (#13 battery).
Didn't see anything at all in the earlier version of Aventa 2.95.
While searching for the programming adaptor, 19902500, I came across an audio shoe, 19901700, sold by Connevans here in the UK and it mentions specifically these two variants (Ambio 77, that is the AM577, & the UP977) but of course no programming adaptor!
Then on another site I came across the same '17' shoe/adaptor wherein it mentioned compatibility and here's where a clue might be given as to why these versions are AWOL! The adaptors are for HAs classified as 'Private' or 'NHS' models .... the only Private model is the 'ReSound Key' series whilst all the others (e.g. Ambio, LiNX3D, LiNX Quattro & Power BTE Range) all come under the NHS!
So are these then all code locked and specifically designed for & sold to the NHS?
Both HAs were acquired on eBay .... the Ambio 77 ones are readily recognised by three of the GN ReSound phone apps namely, Smart 3D, BeMore & Jabra Enhance Pro. After trying many variations/alterations to the Bass/Middle/Treble over several days I finally found a great setting with which I am very pleased .... even better than the professionally programmed Oticon ones I have & very surprisingly different from what I expected, having my Audiogram at hand!
However, since I had hoped to reprogram the UP977's, I contemplated redoing the Ambio 77's at the same time since all the necessary gear required wouldn't even come to half the cost of seeing an audiologist & the hassle of having to try out, & reset, reset, reset until the HAs sound right.
Since the Ambio 77's are good, 'methinks' Murphy's Law is applicable here .... "if it works don't fix it, leave it alone!"
Well, here's another indicator and as yet I'm still left wondering .... the UP977s, with totally fresh batteries, are not recognised by any of the GN phone apps! They look brand, spanking new & work very well but a little tweaking would make them outstanding. So, there are two possibilities, as far as I can determine, at this stage .... they are new & have never been initially set-up which is why they're not found by the apps (?) or they're locked versions!? (NHS)?
Hooking them up to the hardware etc, if the programming adaptors can be sourced, would indicate more, but as pvc has pointed out in his handy DIY School v2.1 conglomeration of PDFs (Unlocking Locked Hearing Aids), unlocking them might not be feasible!
Being able to 'footer' about & find out this much with the software has been an eye opener! Thank-you again for the forum & helping out here.
If I could just get them to be seen by the phone apps they would be manageable that way but ...... !?
Again, any pointers from those more experienced in this domain will be readily received!