Yep the difference between a trifecta and a trio is the same as the difference between an exacta and a quinella.
The trio just involves selecting the first 3 to pass the post, in any order, instead of the first 2 for a quinella.
For the trio you nominate 3 horses to finish in the first 3 in any order.
This costs $1 for 100% of the dividend.
If you box 4 horses in the trio, there are four different combinations of 3 horses available so the trio bet will cost you $4 for 100% of the dividend.
To win the new "double trio" you have to correctly nominate the first 3 past the post in each of 2 nominated races.
If you successfully nominate the winning combination in 1 race but not the other you get zero; you have to nominate the correct combination in both races to get a collect.
To calculate the cost of a "double trio" you multiply the number of different combinations in your first leg by the number of different combinations in your 2nd leg.
For example, if you take 3 horses in the first leg, there is only 1 combination.
If you take 4 horse in your 2nd leg there are 4 different combinations of 3 horses in that leg.
1x4=4, your investment is $4 for 100%.
If you took 4 horses in each leg the cost would be 4x4=16 combinations; $16 for 100%.
You can take any ticket for as little as 1%.