the difference between the HX and TX is the HX is a modular psw and the TX is a hybrid, both offer the same internals, it will probably be hard to dig up a review on them as they are old as the hills now, but still one of the strongest psu's on the market. Whilst they have a 'bronze' rating from memory they were more than up to the challenge of making silver except for draw from memory. Platinum rated stuff i tend to pass on, gold is generally the better product.
major differences between the asrock aside from price, but have the same amount of ports on the back, and it looks like the gigabyte has another usb3 header, but i have always heard mixed reviews on the usb3 controller used on the gigabyte's where the asock's usb3 contollers and software seem to be one of the best for transfer rates. but apples to apples, Gigabyte are one of the best, and their z68 boards are generally fool proof, just trust in the product you know i guess.
last cart looks good, i would double check that the gigabyte board comes with all the usb extensions you will need, and check if the case has usb3 headers in it.