In another universe in which humans may exist but did not evolve, the laws of physics allow phenomena that we in this universe would call magical, where matter and energy may be moved, transformed and manipulated at a distance without passing through the intervening space by interactions of exotic particles that change the way that the usual laws of physics operate.
However, most objects and life forms don't contain any of these exotic particles, and this would include humans. Even if humans could contain - or hold objects containing - such particles, manipulating them in the precise ways necessary for them to cause anything but the simplest magical effects would be beyond human capabilities.
However, humans have discovered the ways that such particles may be generated and manipulated, by observing life forms that did evolve in that universe to be able to produce some 'magical' effects.
This has led to the creation of 'Magic Engines', which are huge, partially organic living, semi-sentient objects that are able to read the intentions of their human creators and operators, and produce magic-like effects upon command, even where their users are a considerable distance from the Magic Engine.
The Magic Engines might draw a small amount of energy from their users as a 'toll' for their use, but would be able to obtain the energy necessary for their tasks from sources external to the users.
Each Magic Engine would have its own way of recognising authorised users, whether by initiation rituals, inherited traits or possession of physical keys or tokens. A person able to use a Magic Engine would be able to do so by virtue of being constantly watched by that Magic Engine in most cases, though some may be able to have their attention attracted to an unobserved user by use of a 'Magical Key', an object that causes an effect that attracts the engine's attention.
Each Magic Engine would have limits on concurrent requests, individual request and total request energy throughout, capabilities and would vary in their command interface and ability to retain user-specific or universally-applicable data.
Some Engines with a highly restricted user base may be able to produce very powerful and optimised effects, while others may have multiple levels of user access, may allow many weak concurrent effects to the general public, may offer increased capabilities to frequent users or may have other individual features. Some may be smarter than others, and can produce more complex effects with less command input than others.
This was inspired by Eliezer Yudkowski's Harry Potter and the Methods of Rationality fan-fiction, but expands upon that work's passing mention of the concept, but this question should not be considered to be about the HPMOR universe.
So, my question is: Is this a workable way of making the quantum-level physics of this universe work as 'classical fantasy' personal magic, and are there any ways in which this idea can be improved?