Can I use a step up transformer?

I wouldn't think you need more gain either, not sure what you mean by overloading your line stage.  If you'd rather have the gain setting you use for phono on the pre match your other sources by boosting the cartridge output, OK, an SUT should work fine.  Just make sure you plug it into the MM inputs on the Chinook, or you will have overload problems.

+1 onywy61 ! Preamps usually sound better when used in the upper range of the volume control!

Matt, I agree with the others that there’s nothing wrong with having to use the volume control in the upper part of its range, as long as you never find yourself wanting to turn it up higher than it can go.

Also, I looked at the specs of all of the components in your vinyl playback chain and I don’t see any way that you could overload anything at any volume setting, aside from possibly driving the amp into clipping in the unlikely event that your ears or the speakers don’t overload first.

Increasing the amount of gain that precedes the line stage from the present 60 db to say 71 db, which could be done by using a 20:1 SUT (26 db gain) into the Chinook’s 45 db MM input would probably result in your using the volume control at not much more than 12 o’clock, rather than at the 3 o’clock setting you mentioned. However it would also result in the possibility that on extremely high volume dynamic peaks on some recordings you might exceed the Jumbo Shrimp’s maximum input spec of 5 volts. (Based on the specs, overloading of the Jumbo Shrimp’s input would occur well before the Chinook would be overloaded). There’s no point to introducing that kind of marginality into your system, IMO.

Regards,
-- Al

What yogiboy and Al said.  The ideal gain structure lets you run toward the end of your line stage's range - all things being equal (which they never are).

Now, from a noise floor perspective, it's possible that a step-up may help, but you'll be dealing with colorations (even with the best of step-ups) that are very possibly a trade-off you won't like.  You will be getting into yet another area where component matching will be critical. 

One overlooked attribute of a step-up transformer is that it works against you from a cable capacitance perspective.  You will have 100 (for a 1:10) or 400 (for a 1:20) times increase in capacitance (the square of the turns ratio) which may or may not matter, but is something to consider when selecting an output cable for your step-up transformer.

So (to equivocate further), it depends ...

Cheers,
Thom @ Galibier Design