Attic mounting adds the negative effect of building materials and does not overcome th effect of weather related impairments. Outdoor mounting is going to provide a more reliable result than indoor or attic mounting in nearly all cases. Metal siding needs to be avoided, it block and reflects signals.
If I were in your situation, I'd point an RCA ANT-751 at the main group of signals (80° compass).
I would use a separate antenna to chase the US stations. The high gain and wide beam of the Antennas Direct DB4e would be my choice. Combining two UHF antennas is not practical for most situations, you may want to consider using this method,
http://forum.tvfool.com/showthread.php?t=2882 I would start with the aim split between S & SW. This antenna needs to be place outside, in the clear, high as safety and practicality allow.
Cable has loss. The longer the cable the more signal is converted to heat before reaching the tuner. RG-6 has about 5 to 6 dB loss per 100'. Splitters are another common cause of signal loss. Typical loss values for splitters are; 2-way, 4 dB. 4-way, 8 dB. 8-way, 12 dB. A preamplifier or distribution amplifier can be used to overcome loss in cable and splitters, but amplifiers do not make a weak antenna stronger. Amplifiers add some noise and distortion, so use one only if the need truly exists.
In the case the weaker signals from the south, an Antennas Direct CPA-19 preamp may be needed.