There are nowhere near the opportunities for gain on the V6 from chiptuning as there are on the diesels. You may get 10-15 BHP.
I'd have a look at the squadra tuning site as they have had a good reputation for not 'overegging' the claims too much, and they have some before /after graphs to compare.
www.squadra-tuning.com
Actually i've just looked and they have no section for the 166..so I'd make an enquiry first just in case.
There is also Autodelta..but they have deleted their 166 mods as well..and they used to do them for sure!!!!
I'm now getting vibes that say the 166 does not have a swappable chip. You have to reprogram the existing eprom,,,so its a remap I'm beginning to think.
AlfaLincs