If you are planning to age for some time, excluding air from the headspace is ideal in order to eliminate the Oxygen in the headspace.
Pouring-in other wine will also add Oxygen and will increase the DO (Dissolved Oxygen) due to the mixing of Oxygen while pouring. Also, there is a fairly high Oxygen Transfer Rate through the cork / cap / crown liner into wine while in the bottle.
By far the easiest way to deal with this is to flush bulk aging vessels with CO2 or N2 for a few seconds prior to filling by siphon. This dilutes the Oxygen concentration significantly, resulting in a much lower DO from racking, and lower O2 in the headspace. FYI, the idea of a CO2 "blanket" is a fallacy - CO2 and O2 diffuse into a uniform mixture in the gas layer above the liquid.
The idea of racking from larger vessels into smaller ones is also sound, although not quite as effective as flushing vessels with inert gas.
If none of these are an option, then treating wine / cider / beer with BOTH Ascorbic Acid AND Metabisulphite at 5g/hL (both) is highly effective at binding free Oxygen that becomes dissolved in the liquid. Note that BOTH is much better than just Metabisulphite, as the two work synergisticly to protect the wine / beer / cider.
If you're not planning to age the wine for very long / plan to drink it within 3 to 6 months, a bit of Metabisulphite is likely just fine.
