sub selects

I hope this is not too confusing..... I left my column names and table names as is but you should get the idea...

I am doing the following:

select usf_fk from am_spots where ams_pk in ((select min(ams_pk) from am_spots where am_fk>135),(select max(ams_pk) from am_spots where am_fk>135);

It works fine but I originally tried this:

select usf_fk from am_spots where ams_pk in (select min(ams_pk), max(ams_pk) from am_spots where am_fk>135);

I received an error saying that my subselect has too many fields. Did I use the wrong syntax or is it just a postgres rule that you can't pull more than one field back in a sub select?

Also, I need to now embed this entire select statement into another select statement such as:

select spot_identifier from al_spots where als_pk in (SELECT STATMENT ABOVE)

Can I do this? Is there any easier way that I cannot see? Any suggestions would be appreciated.
Thanks
Jodi