The latest stereophile has a review of the INT-150, and he does compare it against the XA-30.5 and I beleive the Rogue Monoblocks - so it may be worth taking a browse through that to get an idea of its personality (at least in the reviewers system and opinion).
If you are happy with the Belles sound - matching apples to apples at least in price and upgrade, Belles has the SA-101 and is about $2.5K cheaper then the INT-150A. and about $1K cheaper then the X150.5.
However as Tvad says the final determination would be your ears and what you like.
FWIW - I would invest in a Pre-amp, if it was me :o).
If you are happy with the Belles sound - matching apples to apples at least in price and upgrade, Belles has the SA-101 and is about $2.5K cheaper then the INT-150A. and about $1K cheaper then the X150.5.
However as Tvad says the final determination would be your ears and what you like.
FWIW - I would invest in a Pre-amp, if it was me :o).