In the Complete Arcane, page 9, it indicates:
When a warlock uses both kinds of invocations to alter an eldritch blast, the spell level equivalent is equal to the spell level of the eldritch blast, the level of the eldritch essence invocation, or the level of the blast shape invocation, whichever is higher.
Therefore if a warlock combines Eldritch Chain (Shape – 4th level) as well as Brimstone Blast (Essence – 3rd level), it will be as if casting a 4th level spell if I am understanding correctly since shape and essence levels don’t stack together, and just take the whichever is higher.
Using Maximize spell-like ability on Eldritch blast requires CL to be at least 6 since, Eldritch blast is a 1st level spell and the formula is [(CL/2) – 2].
By that, can a 6th level warlock cast Eldritch Chain with Brimstone essence combined with Maximize spell like ability? Or do I need to re-calculate the spell according to maximize-spell like abilities formula, which would require level 12?