A product they use in many of their works is InkAid. This is a brush-on medium which allows you to print on any surface which will pass through your printer without the loss of colour intensity or durability that is seen e.g. when inkjet prints are made on fine art papers. Sometimes the softer effect you can get by printing on say watercolour paper may be desirable, but at other times it is not. InkAid is the answer to this. BTW I have no affiliation with InkAid(!) I just think its a handy product.
It also allows you to print over collage or mixed media surfaces. This is the process that I have experimented with. I first printed a very low opacity version of my image onto watercolour paper to use as a positional guide. Then I added gesso and artists pencils to achieve a handworked texture. I then applied two thin coats of semi-gloss clear InkAid (my 1 litre bottle is going to go a long way!). When dry I ran the watercolour paper through my printer again, applying the image at 100% opacity this time. Here's the result - hopefully you can pick up some of the textural effects.
Next I thought I'd try a transfer as my initial layer rather than a low opacity print. I thought this would add more character and texture. Using Petitts method, I made my transfer of the sea over a print of the times. I love the rough effect at the edges but a lot of detail has been lost, as you can see (apart from the poor photo - sorry!)
Next I added gesso and artists pencils (below)
Finally I applied the InkAid and running through the printer to add the final layer. Unfortunately I wasn't happy with the result at all! As you can hopefully see from this detail shot (below), I lost the lovely rough edges (of course!) and the effect of the InkAid over the acrylic gel medium that I used for the transfer is quite plastic-y. It really doesn't work with the textural effects I was trying to achieve with the gesso. So... that isn't a process I will be bothering with again. Nevermind, you have to try these things to know.