Well of course there is the question of whether malto-dextrin is the best entity for getting more malt flavor.
I believe it's for body & head and does not give you much at all by way of flavor or sweetness
One way to get more malty flavor is to use more of the darker caramel malt grain.
As you know, they have less enzyme and a darker maltier flavor. Boost the percent of darker malt beyond the normal 10% - 15% to maybe 20% or 30%.
There are products that boost malt flavor like any of the Muntons Malt Extracts (or any malt extract really), a pound of which is supposed to make a lot of difference in flavor, but I think that's for replacing other sugars in an all extract brew. So you know it'll kick the Gravity up.
So, you might experiment with quarter pound increments knowing that the more you use the more you'll need a high alcohol tolerant yeast. And of course you will be getting all the characteristics of the extract brew which you might - or not - find appealing.
If you want more malty flavor why not boost your base grains with more Munich malt. Get some caramel grains and just do a bigger mash, Mash a 5 gallon brew in a 10 gallon tun. With a lot more grain concentrating on the Munich.
Still you are looking at higher gravity but it'll be all grain high gravity.
I've thought a lot about doing something like this trying to get my alcohol up to oh say 16 or 18 percent.
The first ferments would be to the extinction of the beer yeasts ( due to alcohol production) whose flavor I'd want and then the rest of the sugar conversion would be done by adding a neutral Champagne yeast which can go to 18% alcohol.
Down side to that of course is all the alcohol.