Hi Mike,
Good questions only a few of which I can answer. Like yourself I've also embarked on discovering the variations resulting from crossing various color forms of Amaryllis belladonna and Amarygia.
In February 2009, late summer here in the southern hemisphere, I crossed some Amarygia's (including Amarygia Multiflora) with Brunsvigia marginata - the Amarygia being the seed parent. The seed were very small and as you indicated and they were prone to germinate quickly. They weren't as numerous as you obtain from the cross using B. josephinea pollen. In the reverse cross only 4 seeds from B. marginata were obtained from 26 flowers pollinated by Amarygia.
I have been told that similar hybrids made between Amaryllis/Amarygia Multiflora and B. littoralis and B marginata have been flowered by a grower in Tasmainia ( Southern Island state of Australia) with similar outcomes in flower size and color to the josephinea cross. However I have not seen pictures of the flowers to substantiate this observation and even if the flowers are a similar carmine/red color I doubt that the flower count and shape would be identical.
What you call Amarygia Multiflora however may not be the same cultivar type as the one here in Australia by that name. I have flowered a few Amarygia from seed that were given to Australian Amaryllis growers by Les Hannibal. The Hannibal Amarygia's in my collection usually have 16 flowers in a ringlet display, however the Amaryllis Multiflora name was initially given by JC Bidwill to the cross he made between Amaryllis and Brunsvigia multiflora (an early name for B. orientalis) - and this Amarygia can have considerable more flowers (30 to 50). I assume that cultivars of this cross were selected and bred as Amaryllis Multiflora "Rosea" and Amaryllis Multiflora "Alba" over a number of decades.
There were a number of nomenclature name changes given to these hybrids in Australia, and a wholesale Bulb Nursery Holloway Bros. crossed and selected a few named Multiflora varieties during the 1920's to the 1950's.
My question is what do you call the Multiflora types?
Presumably the intergeneric hybrid using B. multiflora (orientallis) when first flowered in 1847 had more flowers than did the Amaryllis x B. josephinea. In Australian Nursery catalogues of the period from 1900 to the 1950's are briefly described a number of Amaryllis Multiflora colour forms - seven of them with specific names - a sample of the descriptions follows: "Handsome crown of pure white flowers - 18 to 24 with delightful perfume" "Magnificant bulb bearing immense heads of rich pink rose fls" "Strong 3' stems with heads of 20-30 deep rose red lilly like blooms"
"huge heads of brilliant cerise pink flowers 30 -40 on 4' stems"
I have 4 different Amarygia Multiflora cultivars - with rose to cerise colours and was recently shown a picture of a 40 flowered white Multiflora cultivar, so although they are rare they do exist and perhaps can be further developed by line breeding.
Over the past two years I have flowered around 60 Amaryllis/Amarygia grown from seed and surprisingly found that about 1 in 8 are superior to both parents. As you commented - it is hard to predict the colour outcomes of these crosses - and amongst these 60 flowered seedlings is a Giant flower form as well as a pygmea sized flower.
Keep in touch.
Jim Lykos
Blue Nountains near Sydney Australia