David,
Is the current sub-base USGA or anything close? Drainage is super important if you want to change to a quality poa free bentgrass green. How high are the salts, we are constantly working with high salt water in Argentina and Chile and there are ways around it. I doubt if there a big issue if the poa is doing ok. You mention you current shallow roots, that is typical of the Poa, no matter what you do, poa will always have shallow roots. My experience is this, if you have a good suib base with good drainage and perculation you are half way there. If the greens are more than 40% poa, which is sound like in your case they are, burn them or gas them but you will need to start over. Depending on the time of the year, you will need, minimum two months to get good coverage and three to four months to have a playable green that will withstand the traffic. You donīt have to eliminate the Poa on the entire course but you will need to incorporate some programs following one year of establishment. Rubigan a fungicide can also act as a seed premergent against the poa but the results will be more in a percentage surpressiing catagory. Velocity as previously mentioned can be used to keep the poa out after the first year. It is important specific programs are followed in relation to the velocity but we have elimated greens with thirty to forty percent poa which invaded the bent during one years time and now are 100% bent again. We are mostly using a mix a mix of A1 and A4 bentgrass, so that helps in the overall programs because of its agressive and dense nature. In conclusion, you are consdiering a major disruption to the playing conditions and will create controversy within the membership. It will also be a significant economic investment. Spend a couple of Grand and hire at least one consultant and get a written report, even better if you have two. The USGA has good consultants and also check in your area for the most experienced consultant. I am confident both will reinforce what I am telling you with some possible additional advice or minor modifications.