I did read somewhere (a few years ago-fading memory) that its better to use the A. palmatum.
When it comes to plant names, the genus Acers is as tough as it gets, and you'll find lots of ambiguity on the net about atropurpureum.
Ive seen it listed as Acer palmatum f. atropurpureum
To the best of my knowledge a forma (the f.= a forma) i.e. Acer palmatum f. atropurpureum CAN be grown from seed.
However, ive done a check on the RHS database, and it doesnt list that plant as a forma.
Theres an entry for:
Acer palmatum 'Atropurpureum'
Quite different.
The single quotes indicate that it is a cultivar.
As you know, you cant grow cultivars from seed, hence one reason why grafting is necessary for propagation.
Hence, it would be much easier to grow Acer palmatum from seed (fairly easy) as rootstock and graft to them, and you'd get a good hit with the seed.
Personally, I'd need to "phone a friend" to get more info on this, Gene. Ive asked Paul (NewPlantGuy).
More later, perhaps.
Input from members would be very much appreciated here...