Oxalic acid is a wonderful tool but use with care as it can turn your nicely coloured wood into a blond nightmare! It is totally dependant on the wood and the stains that have been applied or 'happened'. I always apply with a small brush to already damp wood, not wet or the oxalic can track all over the place.
IMHO, I would never soak a piece in oxalic solution but I bow to the experience of Kutter.
I have found that particular care must be taken around inletting as if the oxalic acid penetrates into the cut end of the grain it can bleach the wood for a few mm's platinum blond!
Traditionally, the treated surface is 'neutralised' with a mild acetic acid solution (I use distilled malt vinegar sold for pickling onions) but I have no idea if this has any useful effect, I just do it anyway!
As regards to 'toners', I am not sure what they might be but I do use water and spirit based stains to colour my restoration projects.
I initially work up a nice orange/brown tone with the Birchwood Casey Walnut stain. I started using this after a very experience stocker friend of mine independently confirmed my person worries that my stock finishes were becoming rather 'grey'. He suggested the BC product as it duplicates the 'orangey' tones of old oxidised linseed finishes. Who was I to disagree?!
I then adjust it using a range of alcohol based stains made by Chestnut. Don't know if they would be available in the USA but they are readily available in the UK.
The advantage of alcohol based stains are that they do not raise the grain and the excess can be washed off with methylated spirits or similar.
I have found that to get a really deep colour it is best to apply some stain, allow to dry and then wash off. Then apply several more coats of stain and again wash off. Repeat until you get the desired darkness AFTER washing off.
Obviously I have to consider the 'red oil' I will apply and stain appropriately. This will redden the overall colour but also lightens it as the wood surface becomes more translucent and allows the light to penetrate.