You can certainly beef up the bio-cycle to be able to process the large bio-load those fish will produce. But you still will have to deal with the end product - nitrate.
The larger tank will help support the nine fish for you with less volume water changes. In a cycled tank, you are changing the water to dilute the amount of nitrate that the fish and cycle create.
The fish produce a given amount of ammonia which is converted to nitrate. With a larger volume of water, that nitrate is diluted out to a lower concentration - one that can be dealt with with fewer water changes.
Example: (ficticious numbers for mathematical ease)
50 gallon tank - 100 ppm nitrate per week
Change 50% - 50ppm
Change 50% - 25ppm
But the fish continue to produce more and a 50% (75%)change is too dramatic. So you end up having to change 30% every 2-4 days just to keep barely ahead of the nitrate.
100 gallon tank - same amount of nitrate= 50ppm nitrate per week
Change 50% and you have 25ppm nitrate. So you can change 30 % of the water every 5 days or so and keep ahead of it.
True - 30% of a 100 gallon tank is 30 gallons, but 30 gallons every 5 days is better than 15-20 gallons every other day, particularly if you are able to utililze a Python or some such labor saving device.
These numbers are pure fiction, but you will be fighting large amounts of nitrate that will never seem to decrease. Large changes every day or two can really get you down.
Besides a big tank is thing of beauty!