I think the difference is the asymmetry that we would place between so called “election” and “reprobation.” Since we press a ‘positive theology’ we emphasize life, the eternal life of Christ as the lens and ground through which we conceive of humanity (his vicarious humanity). So it’s not that we don’t see a need for personal response & faith in order to appropriate the salvation that is the person’s in and through Christ’s Spirit Anointed humanity; instead, it is that we are emphasizing that ‘true humanity’ can only be defined in relation to Christ’s humanity as the ‘original image of God’ (cf. Col. 1:15)—which flows naturally from our ontological theory of the atonement, or, in fact, leads to. And so when we think and speak of humanity we only want to do that in what we have called in the book ‘Christ conditioned’ ways. The fact that some (and even many and most) reject their humanity (and salvation) in Christ, again, from our perspective can only be understood as a ‘surd’ or through the inexplicable nature of sin’s persistence in the ‘Now’. So we hold, as one of our Theses’ asserts, that all of humanity (in redemptive history terms), are ‘carnally’ united to Christ, but not all are united ‘spiritually’ (ultimately). But, again, when we speak of humanity and salvation, in particular, we stress the idea that both carnal and spiritual union between God and humanity has occurred in the vicarious humanity of Christ; and it is through a Spirit created “unioning” with ‘this’ (Jesus’) humanity that the elect say ‘Yes’. So the choice for salvation has already been made for all of humanity, in Christ (from God’s perspective, this is how we understand ‘Pre-destination’ and ‘election’ in Christ); the fact that some reject this, again, is a surd (or absurd) relative to what God has done in Christ (‘for us’).
So the issue has to do with how one conceives of Divine causation, and a certain metaphysics that attends that. We as Evangelical Calvinists (especially Myk and myself) follow Thomas Torrance's rejection of the mechanical, logico-causal and deductive schemata that funds the theology of 5 point Calvinism, for example. So we reframe the discussion in the way that we think the Self-revelation of God does, in Christ; in a Triune, dynamic, personalist, and relational way. We aren't trying to answer the same questions that classic theology does, because we think the questions that shape classic Calvinism and Arminianism are non-starters relative to the faulty starting point they begin from relative to their kind of substance metaphysics.
Cal's question also wonders about, apparently, the sovereignty of God in salvation. In other words, if God has chosen for all of humanity, per the theologic of the incarnation, and in this choosing he has liberated all of humanity to choose or reject salvation in Christ; then how is this any different than an Arminian conception of prevenient grace? This is the point that we must go back to what I just described as logical-causalism, because we (as Evangelical Calvinists) do hold that God in Christ has chosen for all of humanity; we do believe that when and if someone is 'justified/sanctified' (double grace), spiritually, in Christ, that God has brought about this salvation, subjectively, by the Spirit, in their lives. This gets us back to my response to Roger Olson; we think scripture and Christic faith move and breathe in the realm of emphasizing life, God's life in Christ. And thus we believe that the primary emphasis is LIFE not death, such that reprobation is not an viable aspect---only an accidental one---when we articulate our view of salvation. So we are not really far away, at all, from classic Calvinism, in this sense; in the sense that we believe that scripture and God's Self-revelation in Christ demands that the reason the elect are 'saved' is because of God's choice for them in Christ. We don't think that God's Self-revelation in Christ supplies any kind of ontology or theo-logic for discussing WHY anyone is reprobate [except for the intractable and inexplicable reality of sin cf. John 3:16ff] (and so the asymmetry I noted in my response to Roger). And then this, once again, gets us back to what I was noting in regard to our rejection of logico-causal metaphysics. I realize this will not satisfy folk who are committed to using scholastically informed modes of reasoning (which all of Western theology operates from, in general), and that some will assert that us Evangelical Calvinists aren't playing fair; but it is what it is.
Hope this helps, Cal.