Ice:
I am not familiar with that Pyrolox unit you are talking about, however 9gpm flow rate to operate sounds odd to me. I'm guessing it needs that for backwashing the unit properly. The easiest way to check the flow rate of your well is just connect a hose as close to the source as possible, open the it up and let it run into a bucket or two for one minute, and then measure how many gallons came out in that minute. I use a couple of 5 gallon buckets to measure. For example, if it fills one in a minute, it puts out 5 gallons per minute. If it fills one and half of another, 7 1/2 gallons, etc. I can usually guage how many gallons by how much is in the buckets.
I'm guessing your well doesn't put out that much, usually you need a big well pump to put out 9 gpm, and most homes usually have a 1/2 hp pump that puts out 5-6 gals per min or less. Just changing the tank will not increase your GPM, you may have to update the pump, or get a different system for dealing with that Hydrogen sulfur.
40,000 grains for 1 cubic foot of resin sounds strange to me also. Usally 1 cu ft of resin equals 30,000 grain. Unless they have some 'special resin' that has a greater capacity.
40,000 grain is probably a little overkill for 2 adults with that hardness, rule of thumb is 50 gallons per day per adult, so 100 gallons per day, times the hardness of 17, so 1700 grains of hardness per day, with a 40,000 grain softner, you should be able to go 23 days before regenerating! I wouldn't recommend going that long before regeneration, most don't recommend going any more than 10 days. With that metered head it should regen accordingly anyway. If you get that Jacuzzi tub it would add to your total water usage each time you use the tub, so the extra capacity would be nice.--The Captain