AFAIK this is it - the maximum. This is a clickbait, the range will be so small, and the amount of variables is so high, that achieving this is both insufferable and useless. The Buddy/Specter requirement invalidates the build, as it requires another warframe to be configured.

We assume that Nidus with the exactly same build and 5 Amber Tauforged Shards installed, having 475AS, is buffed by:
(Base AS)X2 - Void Fissure
60% - Molt Augmented
50% - Empower
50% - Energy Conversion
50% - Power Drain
50% - Equinox
45% - Molt Vigor
30% - Pax Bolt
25% - Growing Power
Focus Buffs - 40% from Sling Strength of Madurai and 20% of Hardened Wellspring, that our buddy has set up.
The total AS will be 1845%, which results in 461.25% AS Multiplier granted by Parasitic Link.
= BASx2+420

[Wisp], also infused by Tauforged Ambers, having 460% base AS, is being buffed by the Link together with all the buffs [Nidus] was affected by and has total of 3,921.75‬% AS.

[Nidus]: 475+(475x2+420)=1845% AS
(460x2+420)) +460x(1+4.6125))=3,921.75‬% AS