Yes indeed, the Holmboe releases look most interesting

No details given on the Dacapo site for the concertos disc but I presume that we are talking about the 1978-79 Violin Concerto No.2 and the 1991-92 Viola Concerto-which are two of the most important gaps in the Holmboe discography. If so, then bravo

Regarding Bentzon(Niels Viggo that is), where does one start

If it was up to me then I would record Symphonies Nos. 2 and 6, which would fit neatly onto one cd

Those would provide a good introduction to the earlier, more accessible Bentzon.