Hi. I have raised Maltese for over 35 yrs. and five years ago, added one adult female Boxer, Mika. She had been a kennel dog but settled in with the Malts (& other family member's dogs) like she had been raised around them. When I have Malt puppies, she offers to let them nurse (never been a mom), and lays down so they can climb on her and chew on her
A year after I acquired Mika, I got her a sister, Greta. Brought her home at 9 wks. Being a puppy, she had to be trained and worked with to respect the Malts and especially not to play too roughly. That took time. Now, as a 3 yr. old adult, she is super with them.
The main thing is.....the small breeds you mentioned can be fragile, so it is of utmost importance that as far as the Boxers are concerned....the little ones rule the house!! My Maltese rule over the Boxers and the Boxer girls take it
However, they're always under supervision for the most part. That being said....my Malts and Boxers typically curl up with each other to nap, sleep with me, etc. They even play tug of war with each other. In fact, when the Boxers are being fed and a Malt goes up to their bowl (usually under the Boxer), the Boxers will politely back away and let the little ones snitch a bite.
But, the toy breeds do, to a degree have to be protected to make sure the Boxers remember not to box them or get too rough, but it can work.
You may, however, have a problem finding a good toy breed breeder who can be convinced to place a toy breed pup into a home with larger breeds IF they are not familiar with them.