Can't get Domain Mapping to map

Hi there,

I've set up a multisite installation at affilifarm.com and created different sub-blogs on sample1.affilifarm.com, sample2.affilifarm.com, sample3.affilifarm.com etc.

I've registered multiple domains sample1.com sample2.de sample3.com etc. that I want to map to these subdomains.

Domain Mapping on multisite installation is installed correctly, within the sub-blogs admin panels I've set up the mapping.

However, when I check the domains sample1.com, sample2.com etc. I only get "parking pages" as if mapping would lead to nowhere.
When I ping the sample1,2.3...com domains, I get the correct IP of affilifarm.com, however.

Here are the exact specifications:

I've got a SEOhosting account with seohosting.com.
Affilifarm.com is on 69.41.251.34 (dedicated IP), and of course so are the subdomains.

I've set up all domains to be mapped in Tools => Domain Mapping (on sub blogs)

I've tried pointing several domains from different registrars there:

mhs0001.com (registered with SEOhosing, but on a different IP (shared, not 69.41.251.34)
=> Set up A-Record pointing to 69.41.251.34, doing an a record check seems fine

bestehochzeitsgeschenke.com (registered with enom.com)
=> A-Record (@ and www) pointing to 69.41.251.34/

3 different other domains (47zoll.de, 52zoll.de, 55zoll.de)
=> tried pointing A-record to 69.41.251.34, tried setting up CNAME to sample.affilifarm.com

As nothing happened, I also tried setting
Super Admin => Sites => Edit => Site Info (Domain; both siteurl and home) to Sampledomain.com;
however, this does not seem to make any difference.

I'm getting crazy here... could somebody help pleaes?

I'd be happy to provide admin login for both WP as well as hosts (to a trusted developer / WPMUDEV member) to check this...

Thank you so much!
Robert