Improving transient CHO protein expression

[nikinje]

I have started using Invitrogen's freestyle CHO cells (without serum, and in suspension) but the protein expression levels are not great compared to the HEKs I was using before.
I have played around with ratios and have an optimal ratio (1:1 with 1ug DNA and 1ug MAX transfection reagent). I have also tried putting the cells in hypothermic conditions which appears to have increased the expression by almost double, but this still isn't quite enough.

Any other suggestions of something I can do (without extra cloning) to imrpove the expression of the cells?