Generate a table using SUMMARIZE and GROUPBY

Hello

As a relative newbie to DAX, I often find myself going round and round getting tantalisingly close to a solution but missing the knowledge to make things work.  To date, head banging has eventually got me a solution, but not today.

I have a table of Issuers, the relevant fields being IssuerID, Ticker and Analyst.  The same Ticker can be used across multiple IssuerIDs.

I have a table of Assets, with relevant fields of AssetID, IssuerID, Region, Country and NominalAmountUSD.  The join is from IssuerLookup (1) to AssetLookup (Many), on the IssuerID.

My task is to show reports by Ticker, Analyst, Region and Country.  An Issuer can have several Assets and hence multiple region/country combinations, but I'm being asked to extract just one to report on.  The business rule is to use the combination that has the highest NominalAmountUSD - that value comes from a Fact table joined to the Asset table.

I've learnt how to create a calculated table, and that's a good first step.  The following query lets me group across IssuerIDs that share a Ticker:

SUMMARIZECOLUMNS(
    IssuerLookup[IssuerTicker],
    IssuerLookup[Analyst2],
    AssetLookup[Region Of Risk],
    AssetLookup[Country Of Risk],
    "Sum_NV_USD", CALCULATE(SUM(Fact_Assets[NominalAmountUSD]))
)

That gives me good groupings, so the next step is to extract the Analyst, Region and Country for a given ticker where Sum_NV_USD is the maximum.  Having made a virtual table from the query above, called IssuerTickerToCountryOfRisk, the following query finds me the maximum SuNV_USD for a given Ticker:

GROUPBY(
    IssuerTickerToCountryOfRisk,
    IssuerTickerToCountryOfRisk[IssuerTicker],
    "MaxSum", MAXX(CURRENTGROUP(), IssuerTickerToCountryOfRisk[Sum_NV_USD])
)

But I cannot figure out how to combine these to generate a final calculated table that just has the one row per ticker, with the Region and Country coming from the combination with the highest NominalAmountUSD.  I'd like to use CALCULATEDTABLE but the filter argument for that can't use aggregates.  I've experimented with various combinations of ADDCOLUMNS and SUMMARIZE, but without success.

I'd like to have a calculated table in the model with these results so as to refer to it from more than one Power BI Visual.  Any guidance on achieving this will be much appreciated.