6.3 kW 240V Advantium Oven and 4.5kW 140V wall oven hard-wired to 50 amp breaker
This isn't as straightforward as it seems...but it turns out you're OK in the end

The original installer of your oven setup leaned on the NEC provisions for tap conductors in circuits feeding cooking appliances, found at 210.19(A)(3) Exception 1:


  (3) Household Ranges and Cooking Appliances. Branch-circuit conductors supplying household ranges, wall-mounted
  ovens, counter-mounted cooking units, and other household
  cooking appliances shall have an ampacity not less than the
  rating of the branch circuit and not less than the maximum
  load to be served. For ranges of 8.75 kW or more rating, the
  minimum branch-circuit rating shall be 40 amperes.
  
  Exception No.1: Conductors tapped from a 50-ampere
  branch circuit supplying electric ranges. wall-mounted
  electric ovens, and counter-mounted electric cooking units
  shall have an ampacity of not less than 20 amperes and
  shall be sufficient for the load to be served. These tap conductors include any conductors that are a part of the leads
  supplied with the appliance that are smaller than the
  branch-circuit conductors. The taps shall not be longer
  than necessary for servicing the appliance.


This means that the general outline of your setup, while not recommended by the installation instructions for your new oven, does comply with the NEC.  To figure out whether the new oven is allowed, we then turn to Table 220.55, applying Note 3 to the combination load of two ovens, one 6.3kW and one 4.5kW:


  
  Over 1.75 kW through 8.75 kW. In lieu of the method provided in Column C, it shall be permissible to add the nameplate ratings of all household
  cooking appliances rated more than 1.75 kW but not more than 8.75 kW and multiply the sum by the demand factors specified in Column A or
  Column B for the given number of appliances. Where the rating of cooking appliances falls under both Column A and Column B, the demand
  factors for each column shall be applied to the appliances for that column, and the results added together.
  


Given that both appliances fall within Column B, and that the table gives us a 65% demand factor for 2 appliances in that column, this means that while the two appliances sum together to 10.8kW, the Code-computed load on the circuit is actually 7.02kW due to the demand factor. This means that the 40A breaker is sufficient for the circuit, even with the new ovens installed; however, since your wire is 6AWG, you can bump the breaker to 50A safely.