Morning and afternoon all.
I'm not sure if this will work with the IRS as i don't know it would with the UK tax man but all debts are negotiable, i had a £14k debt with a bank that went to a debt collector, they contacted me about increasing the monthly payments so i offered them £5k in one lump sum to clear it all, they said they'd get back to me.
2 days later they phoned back and said they'd accept £7k, i said i couldn't go that far but at a push i could with 6, again 2 days later they phoned back with offer accepted.
Worth a try anyway.